THE PLEISTOCENE OR GLACIAL PERIOD. 363 



sometimes constitutes a more or less well-defined ridge, though this 

 is not its most distinctive feature, since its width is generally great, 

 relative to its height. A moraine 50 or even 100 feet high and a mile 

 wide is not a conspicuous topographic feature, except in a region 

 of unusual flatness. In such situations terminal moraines some- 

 times constitute important drainage divides. 



The most distinctive feature of a well-developed terminal moraine 



Fig. 497. — Terminal moraine topography near Oconomowoc, Wis. (Fenneman.) 



does not lie in its importance as a topographic feature, but in the details 

 of its own topography. Its surface is often characterized by hillocks 

 and hollows, or by interrupted ridges and troughs, following one another 

 in rapid succession, and without apparent order in their arrangement 

 (Figs. 497 and 498). The hollows and troughs are often without out- 

 lets, and are frequently marked by marshes, ponds, and lakes where- 

 ever the material constituting their bottoms is sufficiently impervious 

 to retain the water falling and draining into them. The shape and 

 abundance of round and roundish hills, and of short and more or less 

 serpentine ridges, often closely huddled together, have locally given 

 rise to such descriptive names as the " knobs/ 7 " short hills," etc. 



