79 PALiEONTOLOGY OF NEW- YORK. 



metamorphism. It is only as we approach the zone of great accumula- 

 tion, that we begin to find evidence of metamorphism on a grand scale. 

 In this mountain range, and I believe also in others, the line of meta- 

 morphic action is parallel to the mountain chain, and parallel to the 

 minor elevations or subordinate axes of the great mass ; parallel, in- 

 deed, to the great line of original accumulation of the sediments con- 

 stituting the mountain mass*. 



In accordance with the views I have advanced relative to the accu- 

 mulation of matter along certain zones, and the consequent subsidence, 

 I have also endeavored to reach some explanation for the great extru- 

 sion of trappean matter in certain regions of country. 



The rocks of the Laurentian age, in their great accumulation, are 

 here and there cut by trap-dykes of moderate dimensions ; and the same 

 is true of the metamorphic rocks of pala30zoic age along the Appalachian 

 range, and sometimes "even beyond the limits of the mountain region. 

 The large accumulations of basaltic or trappean matter which are 

 geographically associated with this range of mountains, belong to a 

 later geological period. 



We may not infer, however, from these facts, that there were no 

 extensive outbursts of trappean matter during these more ancient 

 geological periods. In the Lake Superior region, we have extensive 

 trappean accumulations in the period of the Potsdam sandstone ; in 

 Nova-Scotia, during the period of the New Red sandstone ; and in the 

 Connecticut and Hudson-river valleys and elsewliere, connected with a 

 newer sandstone. The great trappean accumulations in the Rocky 



* What I hare here said of accumulation and consequent metamorphism, seems to find some con- 

 firmation in the condition of some of the beds near the base of the Catskill mountains, where, 

 although essentially horizontal, they are nevertheless extremely hard and dense ; having, indeed, 

 more the appearance of a metamorphic rock than many of the beds on the western flanks of the 

 Qrcen-mountain range, where folding and plication are exhibited on a grand scale. Whatever reason 

 there may be for the hardness and density, and the incipient subcrystalline condition of these beds, 

 placed Ijencath more than three thousand feet of accumulated strata, the same beds traced westerly 

 towards the centre of the State do not exhibit the same hardness or tenacity, nor tliat approach to 

 crystalline texture of some of the beds of the Catskill-rttouritairi gt-Oup near the Hudson river. 



