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This study demonstrates how ice-flow history, geochronology, geology, and geophysics may be integrated to enhance the effectiveness of boulder tracing in glaciated regions affected by multiple ice-flow events. Mineralized felsic granitoid boulders (erratics) were discovered 18 years ago on a claim block located 10 km northwest of Little Fort, in the Bonaparte Lake map area (NTS 092P), in south-central British Columbia. Although the boulders have yielded significant gold concentrations (up to 4.15 g/t), their bedrock source is not known. The till near the boulders contains up to 1382 gold grains per 15 kg of bulk material with 75% of the grains having pristine morphology, suggesting a short distance of glacial transport. A U–Pb zircon crystallization age of 198.1 ± 0.5 Ma on one mineralized boulder indicates derivation from an Early Jurassic intrusion. Using a vector addition model based on regional ice-flow patterns, the most recent and detailed bedrock geology map, and recently acquired airborne radiometrics and magnetic data, the northeast sector of the Thuya Batholith (195–205 Ma) is interpreted as the most likely bedrock source of the mineralized boulders.

Analysis of over 10 000 water-well records has been used to produce new depth-to-bedrock maps for areas around five cities on the central Interior Plateau of central British Columbia: 100 Mile House, Prince George, Quesnel, Vanderhoof, and Williams Lake. Hitherto, exploration for mineral and hydrocarbon resources has been hampered by a lack of basic knowledge of the thickness of Neogene and Quaternary lithologies. Interpretation of these new maps provides first-order constraints on the localization of thick drift in pre-Late Wisconsinan bedrock paleovalleys, some of which are now buried. Basalt lavas of the Chilcotin Group are restricted to erosional remnants of previously extensive sheets emplaced onto an older peneplain. Our results confirm that the Neogene and Quaternary cover is primarily controlled by paleotopography and is generally thin and patchy across much of the region. Increased understanding of the three-dimensional distribution of cover produces a corresponding increase in the utility of geological, geochemical, and geophysical exploration techniques, and a reduction in the risk for future mineral exploration activities, especially when combined with more sophisticated data sets.

The relatively subdued topography of British Columbia’s northern interior plains does not reflect the irregular, buried bedrock surface. Many areas have been deeply incised by preglacial rivers that have subsequently filled with a succession of Quaternary sediments. In this study, oil and gas petrophysical logs, drill chip samples, water well logs, and surficial and bedrock outcrop maps were used to model the bedrock topography of the Fontas map sheet (NTS 94I). The modelled data produced several depressions that are interpreted to be paleovalleys incised into the soft Cretaceous shale of the Fort St. John Group. Understanding the geometry, thickness, and stratigraphy of the drift has considerable safety and resource management implications as artesian aquifers and natural gas were encountered in the drift during oil and gas well drilling. Four major paleovalleys are suggested. The most dominant paleovalley (Kotcho–Hoffard Paleovalley) is located south of the Etsho Plateau and trends west-southwest across the map area. A second depression occurs within the loop of the Hay River and may be a tributary of the Kotcho–Hoffard Paleovalley that links with the Rainbow Paleovalley in Alberta. A third paleovalley is mapped south of the Sahtaneh River (Kyklo Creek Paleovalley) and is either a tributary to, or crosscuts the Kotcho–Hoffard Paleovalley. The Niteal Creek Paleovalley is located between the Fontas and Sikanni Chief rivers. Its geometry is speculative as there are sparse data, but it may be a tributary of the Kotcho–Hoffard Paleovalley.

The North Portal for the Edmonton South Light Rail Transit (SLRT) extension is located on the north slope of the North Saskatchewan River Valley west of the High Level Bridge. There was no evidence that the north slope at this location had experienced major, deep-seated slope movements prior to SLRT construction. Since commencement of the North Portal construction, translational slope movements along near-horizontal bentonite layers within the bedrock have developed. Initiation and acceleration of slope movement are believed to be due to the earthwork activities, coupled with precipitation and associated rise in groundwater table. As an interim measure, four deep wells were installed close to the toe of the upper slope in May 1989. The piezometric levels observed after installation of the wells suggest that the drilling of the wells hydraulically connected the various coal–bentonite layers and effectively lowered the higher perched water in the upper coal?bentonite layer. Subsequent slope inclinometer measurements indicate negligible slope movements since the well installations. This paper describes the detailed geotechnical investigations, slope stability assessments, instrumentation, and monitoring records over a 5-year period during and after construction. The paper also describes the implementation of the stabilizing measures and their effects on slope stability. Key words : South Light Rail Transit, North Saskatchewan River Valley, coal–bentonite layers, slope stability, vertical wells.

The paper presents hydrogeologic properties for a leaky till–mantled fractured bedrock aquifer system based on geophysical and hydraulic tests performed at a drumlin located in northeastern Massachusetts, USA. The site profile consists of a fractured bedrock aquifer overlain by a 30 m thick unweathered, coarse-grained till aquitard. Steady state, decadal scale, hydraulics varied little until seasonal irrigation pumping was initiated in recent years, causing a substantial annual drawdown in the aquifer and leakage from the overlying till. High frequency hydraulic head data sets collected in monitoring wells record the hydraulic response to the irrigation pumping. These data sets, together with results from small scale slug and purge tests performed in monitoring wells, are used to characterize the hydrogeologic behavior of this groundwater system. Geophysical logging performed in bedrock wells confirmed the presence of numerous flowing fractures. The large-scale continuum analysis of the fractured bedrock aquifer response to the irrigation pumping yields transmissivity values consistent with those determined from the small-scale, short-term purge test results. The low hydraulic conductivity till has a significant impact on the drawdown behavior of the fractured bedrock aquifer. Calibrated values from the collective data sets and analyses result in the following properties for the 30 m thick unweathered till: hydraulic conductivity K′ = 7.2 × 10−9m/s, transmissivity T′ = 2.3 × 10−8m2/s, and storativity S′ = 2.7 × 10−4, and for the underlying fractured bedrock aquifer: T = 6.5 × 10−6m2/s with an average fracture aperture of 46 μm and hydraulic conductivity Kf= 1.3 × 10−3m/s. These results should describe similar unweathered coarse-grained till–mantled fractured bedrock aquifer systems and provide useful data for preliminary analyses prior to any site-specific investigations.

The erosional impacts of former ice sheets on the low-relief bedrock surfaces of Northern Hemisphere shields are not well understood. This paper assesses the variable impacts of glacial erosion on a portion of Baffin Island, eastern Canadian Arctic, between 68° and 72°N and 66° and 80°W. This tilted shield block was covered repeatedly by the Laurentide Ice Sheet during the late Cenozoic. The impact of ice-sheet erosion is examined with GIS analyses using two geomorphic parameters: lake density and terrain ruggedness. The resulting patterns generally conform to published data from other remote sensing studies, geological observations, cosmogenic exposure ages, and the distribution of the chemical index of alteration for tills. Lake density and terrain ruggedness are thereby demonstrated to be useful quantitative indicators of variable ice-sheet erosional impacts across Baffin Island. Ice-sheet erosion was most effective in the lower western parts of the lowlands, in a west–east-oriented band at around 350–400 m a.s.l., and in fjord-onset zones in the uplifted eastern region. Above the 350–400 m a.s.l. band and between the fjord-onset zones, ice-sheet erosion was not sufficient to create extensive ice-roughened or streamlined bedrock surfaces. The exception — where lake density and terrain ruggedness indicate that ice-sheet erosion had a scouring effect all across the study area — was in an area from Foxe Basin to Home Bay with elevations

The municipality of Metropolitan Toronto (area 480 km2, population 2.15 million) is centrally located on the Late Pleistocene sedimentary infill of the Laurentian Channel, a broad bedrock low up to 115 km wide connecting the Huron and Ontario basins. This channel forms part of a relict (late Tertiary?) drainage network (the Laurentian River) modified by Pleistocene glacial erosion and infilled by over 100 m of glacial and interglacial sediments. The subsurface stratigraphy of the channel fill below Metropolitan Toronto has been established from many different data sources and is depicted, in this paper, as a series of cross sections with a total length of nearly 105 km.The subsurface stratigraphy has been divided, provisionally, into five depositional complexes, which have been mapped in the subsurface along several transects. These are (1) a glacial complex of Illinoian (?) age, (2) a lacustrine complex of Sangamon Interglacial and earliest Wisconsinan sediments (120 000 – 75 000 BP?), (3) a glaciolacustrine – lacustrine complex spanning the Early and Mid-Wisconsinan (75 000 – 30 000 BP?), (4) a Late Wisconsinan (> 30 000 BP) glacial complex, and (5) a postglacial lacustrine complex (ca. 12 000 BP).The data presented in this paper are significant for applied geological investigations in the heavily urbanized Toronto area and provide new insights into the glacial history of the Ontario Basin, in particular the regional extent of the Laurentide Ice Sheet margin prior to the Late Wisconsinan.

The exposures at the St. Marys Cement Inc. quarry at St. Marys, Ontario, have been studied by geologists since the mid-1950s. This paper summarizes previous and new information collected in 2009, 2010, and 2012 and discusses the record of sediments resting on the bedrock surface that have been exposed during quarry operations. The exposed sediments illustrate the dynamic behavior of the Laurentide Ice Sheet in this area during the Late Wisconsin. Evidence for subglacial meltwater activity, shifting ice-flow directions during till deposition, a local or regional erosion event, possible subaerial exposure, and ice-marginal sedimentation is observed in the sequence of tills and stratified sediments exposed in the quarries. It also highlights how rapid lateral facies changes, complex contact relationships, and steep erosional contacts can prove to be challenging for correlation and extrapolation of subsurface units into three-dimensional stratigraphic models. Fourteen units were identified of which the lower six were deposited during the Nissouri age (Catfish Creek Drift). This included five layers of till deposited by a glacier that alternated from flowing out of the Lake Huron basin to that of a regional flow to the south-southwest. An angular unconformity cuts into these sediments and separates them from a finer-grained sediment sequence (primarily of Port Bruce age) consisting of glaciofluvial gravel, two fine-textured till layers, and rhythmically bedded glaciolacustrine sediments, all overlain by the uppermost till, the Rannoch Till, and Mitchell Moraine ice-marginal fan sediments.

Although theoretical models have been developed to predict the location of the failure surface in soil induced by bedrock faulting, no analytical tool is available to estimate subsurface ground deformation. In this paper, a newly developed semi-empirical approach is introduced and developed for calculating surface and subsurface deformations induced by normal faulting in undrained clay. Based on observations from centrifuge model tests, the ground deformation mechanisms are identified by three regions; namely, a stationary zone, a shearing zone, and a rigid body zone. By using an error function to represent vertical displacement continuously, the ground deformation profile can be described quantitatively. It is revealed that the ground deformation profile depends on vertical displacement of the bedrock hanging wall, soil thickness, dip angle of the bedrock fault plane, and a shape parameter that is a function of the undrained shear modulus normalized by the undrained shear strength. Validation and consistent agreement are obtained between calculated ground deformation profiles and other independent centrifuge test results and reported numerical data.

A new tectonic framework for the Flin Flon Belt in southeastern Reindeer Zone of the Trans-Hudson Orogen has emerged in recent years through four-dimensional studies (bedrock and subsurface mapping, seismic reflection profiling, U-Pb geochronology) associated with the NATMAP Shield Margin Project and Lithoprobe Trans-Hudson Orogen Transect. This special issue contains 10 papers covering a wide variety of topics related to the NATMAP Shield Margin Project.

The Bruce Peninsula, a carbonate bedrock escarpment, lies "downflow" from a sculpted bedrock terrain at the French River. The sculpted forms are attributed to a hypothesis of erosion by regional-scale, subglacial meltwater flooding. This paper presents new data from the Bruce Peninsula that tests the meltwater outburst hypothesis in a downflow direction of the predicted flood path. The bedrock surface of the Bruce Peninsula shows extensive development of sculpted features that bear a striking resemblance to s-forms at the mouth of the French River. They are self-similar and hierarchical in scale, ranging in dimensions from a few centimetres to several kilometres. Remarkable concentrations of potholes are located near the brow of the escarpment. The Bruce Peninsula lacks a pervasive cover of unconsolidated sediment. What little sediment exists has been modified into long, narrow drumlins. The Niagara Escarpment on the peninsula has been back wasted into the edge of the Paleozoic Michigan Basin. Along its east-facing slope, the escarpment is marked by more overdeepened reentrant valleys and intervening promontories than is normal for the rest of the escarpment. Clusters of rounded, percussion-marked boulders of exotic origin are concentrated at the heads of the reentrant valleys. Taken together, these features are inferred to support the hypothesis that subglacial outburst floods beneath the Laurentide ice sheet crossed Georgian Bay and strongly sculpted the Bruce Peninsula. The consistent orientation of the reentrant valleys, aligned with the French River sculpting across the basin to the northeast, and the backwasting of its caprock attest to the power and directional stability of the sheetfloods.

The foundation failure of a small earth dam, 4.1 m in height, has created a large breach through the overburden foundation, down to the bedrock, and has produced the complete loss of the Beloeil Lake reservoir. The geological nature of the dam foundation was complex; its resistance to internal erosion has changed with time due to seepage forces. The design of the dam foundation treatment was marginal. In this paper, the conditions of the dam prior to failure are given, the probable causes of the accident are presented, and the environmental consequences are reported. Such a case history of a dam failure illustrates the necessity to have a thorough knowledge of the foundation conditions of existing dams even for a very small water retaining structure. That accident demonstrates also the need for a continuous and effective surveillance program. Damages consist mainly in overburden erosion and sediment transportation through a remote area without any loss of human life. Key words: earth dam, foundation, failure, environment, rehabilitation, dam safety, surveillance.

A sudden increase (outburst) in the seepage discharge was recorded at the downstream toe of dam 3 of the Outardes 4 project. The normal rate of seepage of about 22.5 L/min increased suddenly to 18 000–22 500 L/min. The flow seems to have increased to its maximum rate in a period of not more than a few hours, followed subsequently by a gradual decrease to about 45 L/min in about 20 days.The rockfill dam, with a slightly inclined till core, has a maximum height of about 30 m and rests directly on a very competent bedrock. The quality of the grouted bedrock and the properties of the dam's construction material make it extremely unlikely that seepage through the rock or piping through the core and the transition zones could have caused this event.The presence of a roadfill or "berm" on the downstream rockfill zone, used as a temporary access road during construction and composed of a variety of unselected overburden and rock materials, could have acted as a barrier at the downstream toe of the dam. Thus, the recorded water outburst most likely has been caused by storage of the normal seepage water in the voids of the downstream rock shell and the sudden opening of a drainage channel through this roadfill barrier.Considering the risk of a such ponding in the downstream shell, an emergency drainage system was installed to avoid the repetition of a similar event in the future.The present paper deals with the design and construction of the drainage system whose major component was a tunnel excavated in the bedrock under the dam and illustrates the results of the tests carried out to monitor the ponding tendency in the downstream shell. Keywords: rockfill dam, drainage, tunnel (excavation), blasting (controlled).

Field and associated laboratory experiences with closed-system freezing in earth embankment dams and canals are presented. This type of freezing can cause a redistribution of soil density and moisture, which needs to be considered in the design of soil structures used as water barriers in cold regions. Frost-depth measurements made during the winter of 1978–1979 on two earth dams during interruption of their construction and on the Teton Dam remnant in the State of Idaho, U.S.A., are shown, along with associated soil conditions, air-freezing indexes, and insulating effects of snow and, for one dam, a loose soil cover. Some trends of density and moisture changes near the embankment surfaces were established. Keeping in mind known effects of freezing on soils, the paper raises questions about possible changes in soil density and shrinkage of embankments in contact with bedrock abutments that might adversely affect the safety of earth dams.Key words: dams (earth), canals, frost action, frost protection, soil density, soil moisture, soil shrinkage, soil tests, Teton Dam.

This paper is a review of the design adopted to establish the slopes for deep clay excavations (3 000 000 m3) made for founding rockfill embankment dams on bedrock and for clearing the tailrace tunnel portals at the LG-2 hydroelectric site. The design and excavation of soft sensitive clay deposits down to 22 m had been undertaken at a period of time when very few precedents were existing (1974). During the excavation works, only a few minor slides occurred, indicating that the design approach, using undrained shear strength analysis, was appropriate for the site conditions. Methods of excavation and hauling of material to disposal areas are also described. Key words: slope, sensitive clay, undrained strength analysis, safety factor, excavation method, behaviour.

Deep sockets into bedrock are often used to achieve large capacities for caissons. Most of the available design methods are mainly empirical with little or no relationship to the in situ quality of rock. Bearing pressures and socket skin friction values adopted seem to be conservative in the absence of reliable field information. This paper deals with the problems associated with the design of deep socketed caissons.A concise review of the regional case histories and available design methods involving deep sockets into bedrock are presented. Various methods of testing rock in the laboratory and in the field for obtaining the desired design parameters are discussed. The application of laboratory and field test results in design are given. Problems associated with the construction and inspection of the caissons are summarized.

Within the last few years studies of relationships among faulting, fault creep, and seismicity in active areas such as California and Nevada have progressed rapidly, and have contributed greatly to our understanding of tectonics and the earthquake mechanism. This success prompted a field and literature search for similar phenomena in New York State and adjoining areas, a region of only moderate seismicity but of sufficient population density so that the seismic hazard should be thoroughly studied using all relevant information.Evidence for postglacial bedrock faulting, dated by offset striations, is common on outcrops of a belt of Paleozoic shales and slates that extends from near Hyde Park, New York, northerly along the east side of the Hudson and Champlain valleys, and continues northeasterly into Quebec at least as far as St. Georges. Faults tend to be in the plane of slaty cleavage with the south or east side upthrown in postglacial time. The observed faults are thus high-angle reverse faults with little or no postglacial strike–slip component. Displacement along a single fault is usually of the order of an inch or less, but commonly several such faults are seen in an outcrop only a few feet across. Thus, the faults seem very numerous, and cumulative displacement across a belt tens of miles in width could be quite substantial.An important question is whether this faulting is associated with glacial loading or unloading, with tectonic stresses, or with some other effect such as thermal changes, hydration, or a chemical process in the shales. Present data do not seem adequate to resolve this point, and a major purpose of this paper is to request similar information on other areas, particularly those adjoining the region of interest here. Casual observation of such faults would probably be dismissed by a geologist as slumping, frost heaving, or some other local disturbance in most cases if he were unaware of the regional pattern.Correlation between the pattern of observed faults and that of recent seismic activity is not highly convincing, but this could be because of inadequacies in either or both sets of data, so this question also remains open.

The area that is the subject of the papers by Farvolden and Nunan (1 970, this issue) and by Frind ( 1970, this issue) concerns the southern section of the Welland Canal between Port Robinson and Ramey's Bend, known as the Welland Channel Relocation. The highways and the railway lines will cross the channel on this section in two tunnels, while the Welland River will pass through a new syphon. It compares with six lift-span bridges and a river syphon on the existing Welland Canal. The lowering of the piezometric groundwater pressure along the Welland Channel Relocation was dictated by the decision of the St. Lawrence Seaway Authority to carry out the excavation of the channel prism "in dry" in preference to dredging. The lowering was necessary to safeguard the basal stability in locations where bedrock rises above approximate elevation 495 (ft) (150 m). Bedrock "peaks" occur in three locations along the 8mile (12.9-km) long project at Sta. 75, Sta. 280, and Sta. 430. Out of seven channel excavation contracts, four required dewatering, one of which included the Welland River Syphon at Sta. 38. Apart from the above contracts, two tunnel sites at Sta. 168 and Sta. 293 must also be dewatered. The dewatering on these sites will be perpetuated during the life of the structures. Six pre-design pumping tests carried out by the St. Lawrence Seaway Authority (S.L.S.A.) have indicated a great variation in the permeability and the water-holding capacity of the aquifer. This fact was confirmed by two other