390 



Scientific Geology. 



Little Compton ; but in the intervening space I have never met with 

 any"rocks in place but granite ; and this rarely. For the accumula- 

 tion of diluvium in that quarter of the State is very great ; and, in- 

 deed, the towns of New Bedford, Fairhaven, and Rochester, might 

 be regarded as diluvial without impropriety : but as I have met there 

 with gneiss in some instances, I do not hesitate to represent a deposit 

 of gneiss in those places ; being, however, much in doubt as to its 

 actual limits. 



Almost all the varieties of gneiss that have been described, may be 

 found in the vicinity of New Bedford. In that place it is schistose, 

 and passes into mica slate. There, too, we find a beautiful variety of 

 porphyritic gneiss in bowlders ; the masses of feldspar being flesh 

 red and about the size of a hazle nut. 



Schistose and Stratified Structure : Dip and Direction of the 



Strata. 



In no rock in the State are the slaty and stratified structures so dis- 

 tinctly marked in the same rock, as in gneiss. The strata are usu- 

 ally thick ; and where no local cause of irregularity exists, remark- 

 ably even and continuous. Hence the facility with which the quar- 

 ry men cleave out slabs of gneiss, 20 or 30 feet long, and half as 

 many wide. But these same slabs, when dressed, often exhibit a 

 schistose structure of remarkable irregularity, — the laminae being 

 much bent and composed of different ingredients, so as to give to the 

 rock the appearance of a variegated or clouded marble. The under- 

 pinning of most of the buildings in Amherst, particularly of the vil- 

 lage church, exhibits this appearance most strikingly. The rock, 

 however, will not cleave in the direction indicated by these contorted 

 layers, any easier than in other directions. And hence in strictness 

 of language it ought rather to be regarded as a foliated than a schis- 

 tose structure. Hence, too, this structure does not injure the rock for 

 architectural purposes. 



The following sketch exhibits a very striking case of this foliated 

 structure, as it is developed on the surface of a bowlder, several feet 

 square, lying by the side of the road in Colebrook, Connecticut ; a few 

 miles south of the Massachusetts line. These curvatures are much 

 larger than is usual and more distinct. They appeared to be entirely 

 independent of the stratification. 



