. Elements of geology : a text-book for colleges and for the general reader. Geology. 546 CENOZOIC ERA—AGE OF MAMMALS. Quaternary Period in Eastern North America. I. Glacial Epoch. The Materials — Drift.—Strewed all over the northern part of North America, over hill and dale, over mountain and valley, covering alike, nearly all the country rock, Archaean, Palaeozoic, Mesozoic, and Tertiary, to a depth of 30 to 300 feet, and thus largely concealing them from view, is found a peculiar surface soil or deposit. It con- sists of a heterogeneous mixture of clay, sand, gravel, pebbles, sub- angular s
. Elements of geology : a text-book for colleges and for the general reader. Geology. 546 CENOZOIC ERA—AGE OF MAMMALS. Quaternary Period in Eastern North America. I. Glacial Epoch. The Materials — Drift.—Strewed all over the northern part of North America, over hill and dale, over mountain and valley, covering alike, nearly all the country rock, Archaean, Palaeozoic, Mesozoic, and Tertiary, to a depth of 30 to 300 feet, and thus largely concealing them from view, is found a peculiar surface soil or deposit. It con- sists of a heterogeneous mixture of clay, sand, gravel, pebbles, sub- angular stones of all sizes, unsorted, unstratified, unfossiliferous. The lowest part, lying in immediate contact with the subjacent country rock, is often a stiff clay inclosing subangular stones—i. e., rock-frag- ments with the corners and edges rubbed off. This we will call the " Stony clay " or " Bowlder clay" It is precisely like the ground- moraine of a glacier (p. 55). Over this is often found in places a looser material with angular stones, like the top moraine of glaciers. Lying on the surface of this drift-soil are found many bowlders of all sizes, often of huge dimensions, sometimes even 100 tons or more. The im- bedded subangular stones are usually marked with parallel scratches (Fig. 923), and the large surface-bowlders are usually angular and un-. Fig. 923.—Subangular Stone (after Geikie). scratched. The depth of this material is greatest in the valleys and least on hill and mountain tops. It is difficult, nay, impossible, to give a description of this peculiar deposit, which will apply in all cases. Sometimes scattered about ir- regularly through the unstratified mass are portions which are roughly and irregularly stratified, the laminae being often contorted in the most fantastic way (Figs. 924-926). Sometimes the true stony clay is. Please note that these images are extracted from scanned page images that may have been digitally enhanced fo
Size: 1872px × 1335px
Photo credit: © Paul Fearn / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectgeology, bookyear1892
