E O C i: N E PERIOD. [Ch. XVII I , 



suggested the very natural idea that there existed formerly a 

 chain of lakes, reaching from the highest part of the central 

 mountain-group of France, and terminating in the basin of 

 Paris, which he supposes was at that time an arm of the sea. 



Notwithstanding the great changes which the physical geo- 

 graphy of that part of France must since have undergone, we 

 may easily conceive that many of the principal features in the 

 configuration of the country may have remained unchanged, 

 or but slightly modified. Hills of volcanic matter have indeed 

 been formed since the Eocene formations were accumulated, 

 and the levels of large tracts have been altered in relation to 

 the sea ; lakes have been drained, and a gulf of the sea turned 

 into dry land, but many of the reciprocal relations of the 

 different parts of the surface may still remain the same. The 

 waters which flowed from the granitic heights into the Eocene 

 lakes may now descend in the same manner into valleys once 

 the basins of those lakes. Let us, for example, suppose the 

 great Canadian lakes,, and the gulf into which their waters 

 are discharged, to be elevated and laid dry by subterranean 

 movements. The whole hydrographical basin of the St. Law- 

 rence might be upraised during these convulsions, yet that 

 river might continue, after so extraordinary a revolution, to 

 drain the same elevated regions, and might continue to convey 

 its waters in the same direction from the interior of the conti- 

 nent to the Atlantic. Instead of traversing the lakes, it would 

 hold its course through deposits of lacustrine sand and shelly 

 marl, such as we know to be now forming in Lakes Superior 

 and Erie; and these fresh-water strata would occupy the site 

 and bear testimony to the pristine existence of the lakes. Marine 

 strata might also be brought into view in the space where an 

 inlet of the sea, like the estuary of the St. Lawrence, had once 

 received the continental waters ; and in such formations we 

 might, discover shells of lacustrine and iluviatile species inter- 

 mingled with marine' tcstncca and zoophytes. 



Subdivisions of sfrafu In the J'nnH btisin. The area which 

 has been called the Paris basin is about one hundred and 



