SURFACE GEOLOGY. 6 



scratches have very different bearings, conforming in a rude way to the 

 present topography, and following the directions of the great lines of 

 drainage. In Canada, and in our Eastern and Middle States, these ice- 

 marks are universal. In the Mississippi valley, on certain uplands, like 

 those of the Wisconsin lead-region, no glacial furrows have been discov- 

 ered ; but on most of the highlands, and in all the lowlands, lake-basins, 

 and great valleys, they are distinctly discernible down to the limits 

 specified, if the underlying rock has been such as to retain them. 



2d. Some of the valleys and channels which bear the marks of glacial 

 action— re vide ntly formed by ice, and dating from the ice period, or an 

 earlier epoch — are excavated far below the present lakes and water- 

 courses which occupy them. These valleys seem to form connected lines 

 of drainage at a lower level than the present river systems, and in part 

 lower than the present sea level ; such, indeed, as could not now be pro- 

 duced without a continental elevation of several hundred feet. The evi- 

 dence on which this assertion is based will be cited farther on. 



3d. Upon the glaciated surface we fmd a series of unconsolidated 

 materials, generally stratified, called Drift deposits. Of these, the first 

 and lowest, though not always present, is a tough, blue, unstratified 

 clay, generally thickly set with small stones; more rarely containing 

 those of larger size, ground and scratched. Prom this character it is 

 called the bowlder clay. In the Eastern States, and near outcrops of 

 crystalline rocks, sheets or heaps of gravel and bowlders are frequently 

 found resting upon the glaciated surface. 



4th. In certain localities the pebbly "hard-pan," or bowlder clay, is 

 overlaid by a greater or less thickness of fine, laminated clay, without 

 pebbles. This laminated clay corresponds closely with the " Saugeen 

 clay " of Sir William Logan, but it shades into the bowlder clay below 

 in such a way that it is impossible to draw any distinctly marked line 

 between them. Both the laminated and pebbly clays are, therefore, re. 

 garded as parts of one formation, and the name Erie clay is retained 

 for that, since it was coined by Sir William Logan to designate its 

 exact equivalent on the north shore of Lake Erie. 



5th. On the surface of the clays I have mentioned there is found, over 

 a large area in Ohio and other Western States, a layer of carbonaceous 

 matter, with logs and stumps, and sometimes upright trees. This car- 

 bonaceous layer I have termed the Forest Bed, since it is apparently an 

 ancient soil which sustained a growth of vegetation that covered a large 

 part of the area previously occupied by the ice-sheet. In some parts of 

 southern Ohio this horizon is marked by deposits of peat now deeply 

 buried under the later-formed deposits of the Drift. The remains of the 



