224 



Scientific Geology. 



of the inferior schistose strata, probably by water. There is another 

 fact which the observer will notice in various places on the western 

 declivity of Toby. The thick sandstone and conglomerate strata are 

 often arranged in steps or terraces of great height and thickness. 

 At first view the mountain would seem to have been elevated by suc- 

 cessive throes of some internal force ; each paroxysm throwing up 

 the central part of the mountain higher, and higher, so as to produce 

 these offsets. But there is too much regularity in the stratification 

 to admit of such a supposition. I should rather impute this terraced 

 structure to the action of those currents of water which have exca- 

 vated the valley of the Connecticut. The rock exhibits occasionally 

 cross seams of stratification, nearly at right angles to the surface of 

 the layers : hence currents of water, frosts, &c. would remove suc- 

 cessive portions as wide as these cross strata. On some of the ter- 

 races huge masses of the rock yet remain, raised from their original 

 bed and irregularly mixed, but not far removed. 



It will be seen on the accompanying geological map, that the 

 greenstone ridge which is marked in Sunderland, crosses the Connec- 

 ticut in the north part of that town and then forms its western shore 

 as far north as Gill. The section that has just been given crosses the 

 Connecticut a little south of the place where the greenstone crosses 

 the river ; and consequently the greenstone is represented as on the 

 east side of the river with the sandstone beneath and above it. But 

 north of the place where the greenstone crosses the river, through the 

 the whole extent of Montague and Deerfield, the following section 

 represents the relative situation of the two rocks. 



Now I cannot but regard this fact as some evidence, that the val- 

 ley between Deerfield mountain and Toby, has been to a great extent 

 excavated by water. For I can hardly conceive how so deep a gorge 



