I 



Berkshire Limestone.- 299 



and graywacke,) rest unconformably on the edges of the rocks in the 

 valley of Berkshire, which may pass under this series, as the older 

 mica slate, perhaps, does under the quartz rock and limestone, as ex- 

 hibited on the sketch : or perhaps the rocks of Berkshire valley lie 

 in a basin, whose eastern side is the Hoosac range, and whose west- 

 ern side is the Tacconic range. Then perhaps the transition lime- 

 stone, clay slate, and graywacke, may fill a second basin farther west. 

 Another series, perhaps, was deposited in a third basin still farther 

 west ; and so on till all the earlier rocks are included. 



This view of the case is rendered more probable from a fact which 

 may be learnt by examining the sections appended to this report, 

 (Plates XVII. and XVIII.) that the prevailing dip of the rocks in 

 Massachusetts is towards the east. Why then, it may be asked, is 

 there any more difficulty in regarding the rocks of Berkshire valley 

 as resting unconformably on the older strata, than there is in respect 

 to the new red sandstone of the Connecticut valley, which has an 

 easterly dip, like the subjacent rocks ? The very great difference of 

 mineral character, between the newer and the older rocks of the latter 

 valley, is one reason why we do not hesitate at all to regard the newer 

 as unconformable to the older: whereas in Berkshire, all the 

 rocks appear to belong to the oldest class ; that is, they are highly 

 crystalline and destitute of organic remains. And then the difference 

 of inclination between the varieties of the rocks in Berkshire valley, 

 is much less than in the valley of the Connecticut. Nevertheless, he 

 must be a poor geologist, who does not know that there is often far 

 greater difference in position and mineral character between many 

 members of the primitive class, than between some members of that 

 class and others of the transition, or even of the secondary class. So 

 that the apparently primitive character of the rocks of Berkshire 

 valley, is but a feeble objection against their resting unconformably 

 on those of Hoosac mountain. 



The greatest difficulty which I find in the way of admitting the 

 hypothesis above suggested, lies in the fact, that the change from the 

 older to the newer rocks, as one proceeds westerly across Berkshire 

 county, seems to be gradual : whereas on this hypothesis, we should 

 suppose, that since the rocks dip to the east, the oldest members of a 

 series ought to be found on the western margin of the several sup- 

 posed basins ; and that the change ought to be sudden and great in 

 passing into the basin next west. But so different does the limestone 

 of the western part of Berkshire appear from that in the eastern part, 



