171 



of which they consist, can be traced in every instance to the older 

 rocks of the neighbouring hills inamediately bordering the middle 

 secondary plain upon the northwest; and we can discover a 

 relation between the annount of the several kinds of pebbles, and 

 that of particular sorts of easily abraded strata along the flanks 

 of the valley. Thus, in every case where calcareous pebbles and 

 a calcareous cement are abundant in the conglomerate, the older 

 secondary limestone (Formation II.) may be seen at the base of 

 the adjacent hills, and usually at an elevation that indicates it 

 to have been sufficiently above the weaves to undergo extensive 

 destruction from a sudden and powerful rush of waters. 



In order to account for such a violent denudation along the 

 base of the Highlands, we have only to advert to the state of 

 things attendant upon the outbursting of the trap. This rock, 

 intersecting and overlying equally all portions of the red sand- 

 stone, both its earliest and latest formed beds, was manifestly of 

 simultaneous date throughout the entire region. The violent 

 agitation of the whole belt of country, and the vertical rising of 

 the bed of the red shale valley to a higher level, would necessarily 

 set into rapid motion the entire body of its waters. These, rush- 

 ing impetuously along the shattered strata at the base of the hills 

 confining the current on the northwest, would quickly roll their 

 fragments into that confused mass of coarse heterogeneous pebbles 

 which we see, and strew them in the detached beds of conglo- 

 merate which they now form. The protrusion of the trap, the 

 formation and deposition of the conglomerate, and the elevation 

 and final drainage of the whole red sandstone basin, have hardly 

 been consecutive phenomena, so nearly simultaneous appear to 

 have been these events. The whole time occupied by these 

 stupendous changes must have been extremely brief, compared 

 with the period which produced the main mass of the materials 

 of the basin — the red shales and sandstones — which occupy so 

 large a part of it. 



Of the Middle Secondary Rocks of the Green Pond and Long 

 Pond Mountains. 



When describing the older secondary rocks of the long, straight, 

 and narrow valley which separates the two principal ranges of 



