GLACIO-AQUEOUS ACTION IN NORTH AMERICA. 



207 



8. Contortions of the stratified Deposits connected 

 WITH Drift, 



Mr. Lyell has pointed out several remarkable examples in the 

 drift of Norfolk, in England, of flexures and contortions, in which 

 layers of clay are folded over upon one another for a short dis- 

 tance vertically, while the layers above and below are undisturbed. 

 We have similar examples in the layers of the horizontal clay 

 lying above the drift in our country. Nearly ten years ago I gave 

 in my Report on the Geology of Massachusetts, the section (PI. 

 VIII, fig. 13,) taken from a clay pit in Deerfield. The vertical 

 thickness of the contorted portion is about three feet ; w^iile above 

 and below, the layers w^ere undisturbed and horizontal. 



Since the period above referred to, I have frequently met with 

 similar cases in our clay. And at first view they seem very diffi- 

 cult to explain. But admitting the lakes, wdiere the clay was in 

 a course of deposition, to have existed at the close of a glacial 

 period, we should expect that large masses of ice would have 

 occasionally been carried into those lakes, and very likely par- 

 tially stranded upon the bottom. Suppose them urged forward 

 by the force of winds or currents, while thus partially resting 

 upon the bottom. The consequence must have been, that the 

 laminae of clay, to the depth peneti-ated by the ice, would have 

 suffered a lateral pressure, sufficient no doubt to fold them up and 

 bend them over in the manner shown on the figure ; while the 

 laminae beneath would have remained unchanged ; and when 

 the ice melted away, other laminae would have been deposited 

 upon the disturbed ones in a quiet manner and horizontal 

 position. 



9. Terraced Valleys. 



I am not aware that the phenomena of terraced valleys are 

 different in this countiy from what they are in other parts of the 

 world ; and, therefore, I need not go into a detailed descripfion 

 of them. Where they exist in the greatest perfection, we find 

 two terraces on each side of the river, besides the present banks ; 



