G-eology and Mineralogy. 77 



high latitudes with or without such elevations of land. These 



conditions insure such accumulations of snow above the line of 

 perpetual frost as will sooner or later pass the line of p. ip, mil 

 snow and be changed to ice and water. The water becomes Pa- 

 cini rivers, and the ice will move as a plastic mass to a line deter- 

 mined l.v the amount of snow, on the one hand, and the climate 

 on the other. The advancing movement of the glacier is accom- 

 panied b v erosion and seratehino- of the rocks below and bv the 

 different kinds of moraines, as till or blue bowlder clay, and yel- 

 low unstratitied masses — terminal, lateral, and superficial moraines. 

 Simultaneous with these phenomena we have this action of the 

 glacial river, namelv, a partial denudation of the moraines, and 

 the formation of stratified gravel, sand, and clay. 



The glacial phenomena of the Glacial period were as follows : 

 1. The sinking of the temperature, accompanied by the formation 

 and increase of glaciers; 2. The motion of the ice to its extreme 

 limit; 3. The formation of moraines, of which a part were moved 

 forward and constituted terminal moraines, while another portion 



moi n s. t. flu , ' . TiMMal 



river deposits, or the covering of them bv the glacier itself and its 

 ground moraine. A geological section" of the edge of the ice 

 would then present either (a) pregladal beds; ,/,) stratified gla- 

 ciai deposits p-) a ■''■round moraine; (</') th ic. ' h its terminal 

 moraine: or (</) scratched rocks; (c) a ground moraine; (d) ice 

 and terminal moraines. The first-named section is most common 

 in the portions of Europe covered by Scandinavian erratics. The 

 second is found generally in Scandinavia and in the United 



The retrograde movement of a glacier during the period of 

 melting is characterized: 1. Bv the formations of upper or termi- 

 nal moraines, which are more" or less leveled by local backward 

 and forv, In .vements of a giacict hi ng sucec'ssiv. int n lis ot 

 time ; 2. By stratified river deposits lying upon 



.eled down to great 

 fields containing unstratified materials; (e) stratified beds formed 

 by glacial ri . ■ -<>urces. The charac- 



teristics „f deposits , '... .icinity of high moun- 



tains they contain rote farther away they con- 



sist of deposits of sand and clay. The characteristics of the 

 deposits p.) ;,re: A blue color, due to the seclusion from the oxi- 

 ion of the air; compactness and hardness; rounded 

 form of the bowlders, v " ; ' lU < 



- • 

 led by per- 

 ■.'.-...• - \ .-•.-■. ■ ■, . : --. . ■ r 



angularity of the bowlders, which are rarely scratched, and usually 

 belong to neighboring localities. The characteristics of the de- 



