546 CENOZOIC TIME. 



ble material, made of roots, logs, stems, mosses, etc., blackened but 

 not carbonized ; as, for example, near Cleveland, Ohio, as noticed by 

 Newberry, and near the Grand Sable and Goulais Rivers, as earlier 

 mentioned by Logan. Where clays form the lower deposits, they are 

 generally overlaid by a considerable thickness of beds of sand or sand 

 and pebbles. 



The stratification which the deposits present varies from the most 

 regular, or that of gently-moving waters, to that which could form 

 only under a vast simultaneous supply of gravel or sand and water ; the 

 common form of this Diluvian or Jlow-and-plunge style of deposition is 

 illustrated in the following figure (942), in which the layers are made 



up of wave-like parts, corresponding to 

 successive plunges in the rapidly flowing 

 waters. Beds of this kind occur with 

 others of horizontal bedding ; or some- 

 times locally in the midst of coarse gravel deposits, such stony gravel 

 not participating in it because of its coarseness. 



In many valleys, the formation is the fine-grained non-bedded till, a 

 deposit sometimes of great thickness ; it indicates, by the absence of 

 bedding, that it was made in a prolonged flood, not in violent flow ; 

 for the floods of successive years would have left marks of the succes- 

 sion in the bedding ; and violent movement would have made oblique 

 lamination. 



The stratified beds often have unstratified Drift at bottom ; the latter, 

 in that case, may be a portion of the Drift deposited in the course of 

 the Glacial era, or it may be merely the coarse bowlder part of co* 

 temporaneous depositions, which, because of the size of the stones, 

 sunk at once in the waters to the bottom. It is to be remembered 

 that the larger part of the unstratified beds, with much of the strati- 

 fied, were deposited at the same time, the character of the surface 

 beneath, land, or water, determining the difference. 



The most remarkable of these river-valley formations is that of the 

 great valley of the continent, the Mississippi. As shown by Hilgard, 

 the beds — called by him Orange-sand beds — extend down both sides 

 of the valley, from Kentucky and Missouri to the Gulf ; and, below 

 Natchez, the formation stretches eastward into Alabama, and west- 

 ward into Texas. They consist mainly of sand, but include some 

 pebbly beds, the principal one in the lower part of the valley being at 

 the bottom ; and occasionally they contain, even in Mississippi, stones 

 of ten to one hundred pounds in weight, and rarely one hundred and 

 fifty pounds. There are also some local clayey beds. The stones 

 show that the material came from the northward ; many have in them 

 Paleozoic fossils. The beds have generally the jlow-and-plunge struc- 



