654 LOUIS AGASSIZ, 



ing part of the earth's crust. Now it would 

 greatly facilitate the study of the bottom of 

 the sea if, after ascertaining by soundings the 

 general character of the bottom in any par- 

 ticular region, corresponding bottoms on dry 

 land were examined, so that by a comparison 

 of the one with the other, both might be bet- 

 ter understood. The shoals of the southern 

 coast of Massachusetts have been surveyed, 

 and their position is now known with great 

 accuracy; but their internal structure, their 

 mode of formation, is only imperfectly ascer- 

 tained, owing to the difficulty of cutting into 

 them and examining in situ the materials of 

 which they are composed. Nothing, on the 

 contrary, is easier than to explore the struc- 

 ture or composition of drift hills which are 

 cut through by all our railroad tracks. Now 

 the shoals and rips of Nantucket have their 

 counterparts on the main - land ; and even 

 along the shores of Boston Harbor, in the di- 

 rection of Dorchester and Milton, such shoals 

 may be examined, far away from the waters 

 to which they owe their deposits. Here, then, 

 is the place to complete the exploration, for 

 which soundings and dredgings give only im- 

 perfect information. 



I need not extend these remarks further in 



