68 ILLINOIS STATE ACADEMY OF SCIENCE 



raphy that existed when this particular moraine was 

 built. The moraine then had a greater continuity and 

 greater mass than it now has. When the ice blocks melt- 

 ed, these portions of the moraine lost their identity as 

 elevated parts and became basins which are now the sites 

 of these lakes. 



The concentration of lakes in this part of Illinois 

 raises the question as to why this should be. It is also 

 to be noted that the moraines of this part of the State 

 have a much greater content of stratified gravel than the 

 moraines of the rest of the State, and that the topography 

 is rougher, more hummocky, and possesses more of the 

 kame and kettle features than the rest of the moraines of 

 the State. All of these features indicate that the drain- 

 age from the ice sheet in this territory was much greater 

 than in the rest of Illinois. This was evidently due to 

 two things: (1) The conjunction of the Lake Michigan 

 lobe with the Delavan and Green Bay lobes was such that 

 the radial movement of these ice lobes was opposed to 

 each other, resulting in the ice becoming greatly riven 

 and crevassed, thereby facilitating melting and drainage ; 

 (2) The surface elevation at the conjunction of 

 these lobes was lower than that of the summit 

 of either lobe, hence there was concentration of 

 drainage from the surface of any two adjacent 

 lobes. With great quantities of water, therefore, pour- 

 ing forth from the ice sheet in this territory, the finer 

 materials of the glacial debris were carried away, leav- 

 ing the coarser materials deposited in the form of sand 

 and gravel hills commonly known as kames, and in the 

 form of outwash plains and valley trains. 



What has been said thus far in regard to the lakes in 

 the morainic belts does not apply, however, to such lakes 

 as Crystal Lake. This beautiful body of water does not 

 lie in a terminal moraine; it is surrounded by an out- 

 wash plain. It appears to have originated from a de- 

 tached block of ice, a mile and a half in length and a quar- 

 ter of a mile in width, having become detached in the 

 recession of the ice and surrounded and buried by the 

 outwash gravels, later" leaving a basin for the inunda- 

 tion of the lake water. This general territory in fact is 



