146 



Scientific Geology. 



entirely covered by a thick coat of diluvium of a similar character j 

 and so is the whole coast, from Cape Cod to Rhode Island, except 

 that south of Rochester there is much less of sand ; but the quantity 

 of bowlders is prodigious ; so that one often travels many miles with- 

 out seeing a rock in place ; although the surface is almost entirely 

 covered by rounded masses of almost every size. This is seen on 

 almost any road from New Bedford to Rhode Island. 



Passing northerly from Buzzard's Bay, the whole country east of 

 a line drawn from Providence to Boston, except the summits of a few 

 of the highest mountains, and some alluvial valleys, is covered with 

 diluvial blocks and gravel. But from Boston to the extremity of Cape 

 Ann, embracing a considerable proportion of Essex County, the 

 amount of bowlders is prodigious ; and some of them are not less 

 than 30 or 40 feet in diameter ; and yet so powerful was the diluvial 

 current, that these must have been removed from their original posi- 

 tion, and many of them now occupy the summits of the highest hills 

 in that region ; presenting often a most singular outline to the land- 

 scape. When one of these erratic blocks is so poised upon a rock in 

 place, as to be easily moved, it constitutes a rocking stone. Some of 

 these, weighing from 10 to 100 tons, can be perceptibly moved by the 

 strength of a single man, applied to a lever ; though the combined 

 efforts of a hundred men cannot move them but a few inches. Of 

 two of these rocking stones I have taken a sketch, on account of their 

 peculiar appearance. 



Rocking- Stone in Chelsea. 



The preceding sketch represents a mass of porphyry, 10 or 12 feet 

 in diameter, lying on a ledge of the same kind of rock in the north 

 part of Chelsea, near the toll gate, on the Newburyport turnpike. The 

 following is a view of a divided block of gneiss, which is nearly 10 

 feet high, and is so accurately poised upon a ledge of gneiss, that at 

 a little distance it seems as if it could easily be thrown over ; but this 



