212 



Scientific Geology. 



trap rocks ; as at Turner's falls, and on both sides of Holyoke and 

 Tom. It is made up of coarse gray sand — sometimes of comminuted 

 granite entirely, as on Holyoke — and varies in color from light to 

 dark gray. In some localities, as in Granby, the strata are thick, 

 and the rock is scarcely schistose ; it is there used in architecture. 

 In other places, the strata become thinner. On the banks of the 

 Westfield river, in West Springfield, I noticed a variety that resem- 

 bles the grindstones brought from Nova Scotia, though it is harder. 



Gray micaceous sandstone. When the last variety takes mica into 

 its composition, it becomes more easily divisible into laminae ; and 

 where that mineral abounds, it is very fissile. Some specimens of 

 this kind, found in the vicinity of trap rocks, can hardly be distin- 

 guished, in hand specimens, from mica slate. (Nos. 177, 178, 179.) 

 Gray micaceous sandstone abounds at Turner's Falls, on Mt. Toby, 

 in South Hadley, in West Springfield, &c. 



Variegated sandstone. This is composed of alternating laminae 

 of light and dark red sandstone, usually somewhat micaceous. The 

 layers are not very evenly arranged ; so that their edges present rath- 

 er a fantastic appearance. I have scarcely met with this rock except 

 on the banks of Westfield river, half a mile west of the village of 

 West Springfield ; where the characteristics of the new red sand- 

 stone are more fully developed than any where else in the valley of the 

 Connecticut. The variegated sandstone there forms thick and work- 

 able strata. 



Brecciated Sandstone. This is composed of fragments of micaceous 

 sandstone, which seem to have been partially fused and then reunited. 

 It is almost as hard as siliceous slate. It is found about a mile east of 

 Turner's Falls, on both banks of Connecticut river, forming a stratum 

 some 20 feet wide. The stratification and schistose structure are very 

 obscure : but on the north shore, the layers have evidently been forced 

 upwards, so as to give them somewhat of a spheroidal form. I 

 hence infer that a mass of unstratified rocks, probably greenstone, lies 

 beneath the sandstone at no great depth ; and that when this was forc- 

 ed upwards in a melted state, it partially fused the sandstone. (No. 174.) 



Red micaceous sandstone is not unfrequently a member of this for- 

 mation. The grain is usually fine, and indeed, it commonly ap- 

 proaches very near to shale, into which it passes ; yet much of it is too 

 coarse and contains too much siliceous matter to be called shale. It 

 is very common along the east side of our greenstone ridges, as at 

 Turner's falls and in West Springfield. It is quite remarkable for be- 



