548 



CENOZOIC TIME. 



nature. But where the river terraces are extensive, the coarse, low- 

 est bed is seldom in sight, because far too deep for observation except 

 through the sinking of shafts. Either side, approaching the hills which 

 bound the terrace-formation, the depth is less, and often a few yards 

 down, scratched bowlders may be found abundantly. But in the parts 

 of large valleys where the depth of the water was small, the cobble- 

 stone and bowlder deposit may be in sight, constituting a low terrace 

 along the river valley, or the under portion of the other terrace de- 

 posits. Long lines of such coarse and often only semi-stratified mate- 

 rial occur along the upper half of the Connecticut and on other rivers 

 and have been called by the Scotch name kames. 



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 flow-and-plunge style of deposi- 

 tion is illustrated in the following figure (945), in which the layers 

 F j„. 945 are made up of wave-like parts, corre- 



sponding to successive plunges in the 

 rapidly flowing waters. Beds of this 

 kind occur with others of horizontal 

 bedding ; or sometimes locally in the midst of coarse gravel deposits, 

 such stony gravel not participating in it because of its coarseness. 



In many large valleys the formation is the earthy loess, a deposit 

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

 that it was made in a prolonged flood with the waters comparatively 

 quiet, and not in violent flow; for the floods of successive years would 

 have left marks of the succession in the bedding ; and violent move- 

 ment would have made oblique lamination. (See further, p. 660). 



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 flow-and-plunge struc- 

 ture, illustrated in Fig. 942. The facts prove that there was a vast 

 and violent flow of waters down the Mississippi valley, bearing an 

 immense amount of coarse detritus ; a result commensurate with the 



