OX THE FORM ATI OX OF LAKES. 543 



It may be urged that these beds of clay, with their striated stones 

 and huge bowlders, are found over a large section of our country, and 

 are not confined to the region of the lakes. This is very true ; and 

 from it we conclude that where now so many happy homes are scat- 

 tered, from Maine to the far West, the snows and frozen mists of a 

 great winter once accumulated to many thousand feet in thickness, 

 and formed a great glacier, like that which covers the interior of 

 Greenland at the present day, which flowed southward, grinding 

 down the country and acting as a ploughshare to prepare the land for 

 a new harvest. Gradually this great winter began to pass away, and 

 the spring-time in which we now live, to draw near. As the great 

 glacier retreated northward, it left the country covered with beds of 

 bowlder-clay and strewed with huge erratics from northern regions, 

 which together with other debris form the surface material of all our 

 northern country, where it has not since been swept away or covered 

 by other and more recent deposits. It is often well exposed along 

 our lines of railroads, and may be known at a glance by the great 

 number of worn and rounded stones of all sizes that are scattered pro- 

 miscuously through it. These evidences of glacial action are found 

 as far southward as Cincinnati and the central portion of New Jersey, 

 showing that here was the border of the icy mantle that was spread 

 over all the northern regions. After this great continental glacier 

 passed away, or had retreated far northward, smaller and detached 

 streams of ice still flowed southward to complete the task of moulding 

 the valleys and lake-basins. It is to these smaller glaciers that we 

 attribute the formation of the multitude of lakes filling rock-basins 

 that are scattered through the northern part of the United States and 

 over the whole of the British possessions, many of which have been 

 hollowed out in nearly horizontal beds of rock in the same manner as 

 lake-basins are now forming under existing glaciers. Nor are the 

 lakes which fill glacier-worn rock-basins confined to our own continent, 

 but they form the most common and grandest lakes of temperate lati- 

 tudes, which might be called the lake latitudes, so completely are the 

 lakes of the world confined to these regions. 



The theory of the glacial origin of certain lakes was first proposed 

 by the distinguished English geologist, Prof. Ramsay, and, after being 

 tested in nearly every glaciated region in the world, is now held, by 

 those best qualified to understand it, as the simple and true history 

 of the formation of many of our lakes. 



2. The lakes of our second class, those which are confined by 

 banks of gravel, bowlders, etc., owe their origin, like the ones we have 

 been considering, to the action of ice. Lakes of this class are most 

 commonly found in the deep Alpine valleys of mountainous regions, 

 where the material which accumulated on the surface of the glaciers 

 that once flowed through them, in the form of lateral and medial 

 moraines, was carried down and deposited at the extremity of the 



