236 W. M. Fontaine—Mesozoie Strata of Virginia. 
often traveled 100 miles and more measured in an air-line, and 
much farther, if the course of the rivers crossing the Blue Ridge 
be followed. Professor Rogers in the old survey of the State, 
noticed these clays and expressed the belief that they must 
General remarks and Conclusions.—It is a noteworthy fact 
that the belts of Mesozoic which yield coal, contain it mainly 
at their southern or higher extremities. This is true of the 
once in the earlier periods, but did not penetrate to the sea. 
Toward the close of the Jurassic they advanced in such force 
that they reached the sea. In the intervening time, while the 
ice was gathering force, ice rafts, charged with stones and earth, 
floated down the streams which issued from the foot of the ice. 
To the frequent pushing forward, and consequent abrasion 0 
the matter accumulated at the foot of the ice, and in the upper 
course of the rivers, we must attribute much of the rounded and 
lished condition of the Potsdam stones now found so far to 
the east of their original position. This ice may have made its 
nal advance over the whole of the portion of the Atlantic 
slope in which the features above described are found, or It 
may have issued from the Blue Ridge, mainly along the line 
of the Potomac and James, and then in its farther advance to 
