Diluvium. 



153 



have been transported in a direction a little south of east, in order, to 

 reach the west part of the Vineyard, where I found them. 



We shall rind abundant confirmation of this opinion in respect to 

 the last named rock, if we pass from New Bedford to Rhode Island, 

 either close along the coast to Little Compton, or farther north, to 

 Tiverton. The surface is covered with bowlders, chiefly of granite 

 and gneiss. But occasionally we meet with masses of the conglom- 

 erate, whose diameter varies from one to twelve or fifteen feet. And 

 by inspecting the map, we shall see that the gray wacke formation, 

 from which they must have been derived, is very extensive in a north 

 and north west direction. Can there be a doubt that such was the 

 origin of these blocks ? If it was, then the diluvial current must 

 have been powerful enough to move masses of this size, in some in- 

 stances, not less than twenty miles. The region of country interven- 

 ing, however, is not very uneven ; and in estimating the power of 

 running water to move rocks, we ought always to bear in mind, that 

 they are but little more than half as heavy when immersed in water 

 as in air. 



Another instructive region, in respect to erratic blocks of gray 

 wacke conglomerate, lies on the east side of Taunton river, in Free- 

 town and Troy. Along the river road the bowlders of this rock 

 greatly predominate; and yet I could not find any of it in place: but 

 the rock there, so far as I could ascertain, is granite. These blocks, 

 therefore, must have been transported from the opposite side of the 

 river, in a south or southeast direction, in order to have come from 

 a gray wacke deposite. 



In several places, as may be seen by the map, the tracts of gray 

 wacke are bounded on the north by primary rocks ; chiefly sienite, 

 granite, and greenstone. And as we approach these primary rocks, 

 from the south, even when eight or ten miles distant, Ave begin 

 to find their rounded fragments ; until at length, and that often at the 

 distance of two or three miles from the primary ledges, they equal, 

 or exceed in number, those of the gray wacke ; rendering it often 

 exceedingly difficult to ascertain the boundaries of the different for- 

 mations. But on the other hand, no bowlders of gray wacke are 

 found in the primary regions, lying north of the gray wacke in place, 

 except those very rare stragglers already alluded to ; whose situation 

 can be explained only by supposing a previous deluge in a different 

 direction. 



I think, however, that no geologist can examine the surface of the 

 20 



