374 GEOLOGY OF OLD HAMPSHIRE COUOT^Y, MASS. 



gi-ation of the rocks (as insisted upon recently by Professor Pumpelly and 

 applied by liim to a more ancient transgression),' especially the vast amount 

 of granitic debris, which has been swept into its place so rapidly that, 

 although carried many miles across the valley, it is so angular that it seems 

 to be still at the base of the granite ledge from which it was derived. 



I have been further led to look with some hope upon the theories con- 

 cerning former high tides and strong ' tidal currents which have been so 

 eloquently expounded by the astronomer. Sir Robert Ball,^ for it is beyond 

 question that the sediments were spread by tidal currents which passed 

 north up the west side of the valley and down the east side, and with a 

 force greater than I can find anywhere described for modern currents. 

 The proof of this is jjresented here in abstract, but many details are given 

 in the description of the different rocks in the last chapter. 



Along the middle portion of the western border-lands of the Triassic 

 basin is a very great development of granites, abundantly musco^•itie, and 

 the schists down to the southern line aboimd in these dikes, which plainly 

 extend eastward far beneath the border of the Trias. Now, all along this 

 line the Trias is made up at the shore-line of a granitic conglomerate which, 

 as it extends far out into the valley and up in the series, graduates through 

 coarse to fine arkose. 



In the northern half of the State the western border-country is of 

 black schists and argillites, but the arkose sweeps up along this shore for 

 more than 20 miles, scarcely darkened by any admixture of the black 

 schists, but where it is coarse containing many large, well-rounded pebbles 

 of the vein quartz from the schists. Here it is plain that the immediate 

 shore wash has rounded the quartz pebbles, and that they have then been 

 carried outward by the undertow and forward diagonally by the sweep of 

 the tidal current, while the mass of the material came from much farther 

 south. 



The same thing is clear along the eastern side of the valley. The 

 materials derived from each of the rocks that formed the ancient shore are 

 carried far south of the area occupied by the respective rock. At the 

 north end the peculiar crystalline rocks of the Northfield hills form 

 the slate-conglomerates at their foot and are carried far south. And 



'Secular rock disintegration: Am. Jour. Sei., 3d series, Vol. XVII, 1879, p. 133. The relation 

 of secular rock disintegration to certain transitional (rystalline schists: Bull. Geol. Soc. America, 

 Vol. II, 1891, p. 209. 



- A glimpse through the oorridors of time: Nature, ^■ol. XXV, p. 79. 



