Near Woodbridge, northwest of Toronto, Ontario, a 15 metre-high railroad cut and associated borrow pit, first excavated in 1962, exposed a multiple till sequence and intervening fossiliferous sediments. Work over the next 35 years revealed that Illinoian York Till, early Wisconsinan Sunnybrook Till, and late Wisconsinan Humber till, Halton Till, and Wildfield Till are interbedded with fossiliferous sediments equivalent to the Sangamonian Don Formation, early Wisconsinan Scarborough Formation (>50 ka BP), and middle Wisconsinan Thorncliffe Formation (45 ka BP). A complex periglacial record displays multistage fossil frost wedges, indicating intervals of severe climate in late Illinoian and early Wisconsinan time. Cored boreholes indicate deep gravel below and a till on Ordovician shale bedrock (Georgian Bay Formation). Vertebrates, molluscs, ostracodes, insects, and plants (diatoms, wood, seeds, pollen) indicate mostly cool conditions (boreal to tundra) for interstadial sediments. Interglacial conditions are represented by vertebrates, molluscs, and plants above York Till. Many taxa are new to the Quaternary of the Toronto area.

The geologic and geotechnical characteristics of thick soft Champlain Sea clay deposits at Hawkesbury, Ontario are presented in this paper. A second paper will deal with the mineralogy and geochemistry of the same deposits.A westerly clay plain at ~50 m and an easterly plain at ~75 m elevation occur in the area. Preconsolidation pressure versus depth curves obtained for clays from both deposits show marked preconsolidation near the top and bottom drainage boundaries and nearly normally consolidated conditions at the centre. This suggests that both sites were loaded by sandy fluvial (deltaic) sediments that were eroded ~70 years after deposition, an ancestral meander of the Ottawa River being responsible for the erosion on the lower clay plain. Two stratigraphic schemes compatible with the σP′ versus depth profiles are presented. For the lower elevation clay plain these schemes suggest erosion of 21 m of deltaic sands, a value generally confirmed by field studies of deltaic sand terraces to the west.The sensitivity of the lower level clays decreases from ~25 at surface to ~5 at depth. The upper level clays are very different, having a maximum sensitivity of ~20 at mid-depth and decreasing towards the top and bottom. These trends reflect differences in the liquidity index for both clays and in salinity for the lower level clays. The low values of sensitivity relate to the relatively high clay mineral content of 51% and salt content of 1–20 g/L measured on these partially "leached" clays. Keywords: Champlain clays, preconsolidation, diffusion, erosion, vane strength, salinity.

No abstract

The potential for lateral instability of highly stressed, near-surface sedimentary rocks such as the Paleozoic deposits of southern Ontario and western New York State is investigated analytically. The minimum magnitude of the in-situ stress required for a pressure ridge to form is easily computed once values are obtained for the stratum thickness and short-term Young's Modulus, the weight of overburden, and the residual friction with the over- and underlying material. Consideration is also given to the increased likelihood of instability associated with excavations of different widths and depths. Keywords: rock, excavations, quarries, instability, pressure ridges, mechanisms.

No abstract