OR UPPER BARRIER. 335 



Great masses of primitive rocks from the demolished 

 mound or dam, and vast quantities of sand, mud and 

 grave], were carried down the stream to form the curious 

 mixture of primitive with alluvial materials in regions 

 below. 



2. The breach at the northern extremity of lake 

 George. 



It may be presumed that the pressure of water conti- 

 nued for ages, finally demolished the barrier near the 

 outlet of lake George. The sea must have subsided to 

 the level of the breach, and the lake been diminished to 

 about its present size. A part of the geological configu- 

 ration in that neighbourhood may be traced in all proba- 

 bility to this source. 



3. The breach made by the Hudson at Hadley Falls. 



On ascending the Hudson, the traveller finds the coun- 

 try, as he approaches the cataracts of the Hudson, called 

 Glen's and Hadley's Falls, composed of alluvial mate- 

 rials, mingled with detached masses of primitive rocks 

 removed from their stratified beds. The quantity of this 

 loose matter is so great, as to cause the name of Sandy- 

 Hill to be given to the place where It is most abundant. 

 But on exploring the river a few miles above Sandy-Hill, 

 the marks of violence and disruption present themselves. 

 The beholder becomes satisfied whence the loose mate- 

 rials came which he surveyed on his approach. They 

 consist of the fragments of the broken barrier and of the 

 sandy alluvion forced down the stream when the dam 

 gave way. 



In this case tfre primitive fragments and the alluvial 



