Boston Harbor. 125 



ones, nearly as far as the Boston Light, being composed chiefly of 

 diluvium ; though on their shores, at a low level, not unfrequently 

 we find argillaceous slate and other rocks that occur on the main 

 land. But all the islands outwards from the Great Brewster, are 

 merely naked masses of rock, and it would be natural to infer that 

 the diluvium had been removed from these, even if we did not actu- 

 ally detect the process. But on the Great Brewster, the work is go- 

 ing on before our eyes. Its eastern side is a high bank of diluvium, 

 obviously wasting away by the action of the waves that roll in upon 

 it from the wide Atlantic ; while the extensive beach along its south- 

 ern side, is composed of the materials that have been swept away 

 from its outer coast. The same process is seen going on upon the 

 outer side of several other islands j and on Deer Island an extensive 

 wall of stone has been erected by the U. States Government to arrest 

 the progress of this degradation ; which, if continued much longer 

 there, would lay open the inner part of Boston Harbor to the fury of 

 the northeasterly storms. From the same cause another of these Is- 

 land, (I have forgotten which,) when seen 

 from the northeast, exhibits an outline as 

 regular, and with a single house near its 

 center, as fantastic as this drawing. 

 It seems to me that no man, accustomed to reason correctly from 

 geological facts to their causes, can hesitate, in view of the appear- 

 ances which these islands exhibit, to infer that all those outside of the 

 Great Brewster have been deprived of their diluvial coat by the ac- 

 tion of the ocean. Nor when we consider the frequency and vio- 

 lence of northeast winds and storms upon this coast, need we fear 

 that the cause is inadequate to the effect ; although it is not less than 

 two and a half miles from the Great Brewster to the outermost of the 

 Graves. It does not, indeed, follow, that all the intervening space 

 between these outer islands was once solid land ; so that the ocean 

 has actually worn away 21-2 miles ; and yet, this seems highly 

 probable. Indeed, the mind is irresistibly led to enquire whether the 

 whole harbor has not been thus produced by the same cause ; and 

 when we see so many islands scattered over its bosom, which seem 

 obviously the wrecks of one continuous diluvial formation, and per- 

 ceive that the rocks, wherever they occur, are only a continuation of 

 those occurring on the mainland, the most cautious reasoner can hardly 

 avoid the conclusion that such was the origin of this harbor : or, at 

 least, that this was a powerful auxiliary cause in its formation. Nay, 



