REPORT OF THE SECRETARY. 35 



museum of the Smithsonian Institution, weighs 3,000 pounds, pre- 

 senting angular points. 



One of the characteristics which denotes the unity of the drift 

 is the presence of wood, leaves and other vegetable matter. The im- 

 ™ bedded timber is the same throughout the formation and is similar to 

 that of the present growth of a more northern latitude, consisting of 

 pine, spruce, willow, and white cedar, the latter being most abundant. 

 At Cleveland, Ohio, the entire trunk of a white cedar, twenty feet in 

 length, filled with proto-sulphide of iron, was found imbedded in the 

 drift eighteen feet below the surface, and many wells in that city are 

 rendered unfit for use by the layer of vegetation through which the 

 water passes. 



Animal remains, such as those of the elephant, mastodon, and horse 

 are found in the same formation, in addition to various varieties of 

 fresh- water shells. 



Through the western country there are bluffs and terraces com- 

 posed of solid rock, but besides these "there are others composed of 

 boulders, gravel, hard-pan, clay, or sand. The former were the re- 

 sult of geological causes more ancient than the drift, while the latter 

 are contemporaneous with this formation, and are probably due to 

 parallel currents. What are commonly known as lake ridges, accord- 

 ing to the author, are not ancient beaches, but the result of lateral 

 currents distributing the drift. All the rivers and streams cut through 

 these ridges and exhibit the drift clay frequently down to the rock 

 below, while the beaches evidently belong to the alluvial period. 

 Ancient lake ridges must not, therefore, be confounded with lake 

 beaches. The distinctive feature of the latter is that they are narrow 

 and steepest on the lake side, resembling terraces. 



In the prairie region of Illinois, Wisconsin, Iowa, and Missouri the 

 general surface is very uniform, but little elevated above the north- 

 ern lakes. A rise of only twenty-six feet in Lake Michigan would 

 turn its surplus waters across the summit into the Illinois river. Over 

 a territory embracing Ohio, Indiana, Illinois, Iowa and part of Ken- 

 tucky, Tennessee, Missouri, Wisconsin, Michigan, and Canada West, 

 there are no considerable elevations. This space is an extended 

 basin with a rolling surface, in which glacial action, unobstructed in 

 § its movement, would tend to produce but little change in the general 

 topography, and therefore the position of valleys, rivers, and lakes 

 is about the same at present as it was before the glacial period. 

 The motion of the ice, however, must have removed a large portion 

 of the broken fragments of the northern rocks to positions further 

 south. The appearance would indicate that, as the glacial period 



