Supposed Volcanic Agency. 



203 



summits. Such facts have opened a new field for chronological geol- 

 ogy ; and in*our country it is as yet entirely untrodden. 



Although the newest tertiary in this State appears to have remained 

 undisturbed since its deposition, yet it is interesting to find that our 

 plastic clay has experienced a convulsion, almost equal to that by 

 which its strata, in the Isle of Wight, have been thrown into a verti- 

 cal position.* As to the period when the strata at Martha's Vineyard 

 were elevated, I can say but little. I have already expressed an opin- 

 ion that a granite ridge passes along the western side of that Island, 

 not far beneath the surface: But I have searched in vain there for 

 any of the more recent unstratified rocks. At present, then, I must 

 conclude that we have no evidence of the action of any disturbing force 

 since the protrusion of this granite. But in Europe, I believe no 

 rock above the chalk has been proved to have been disturbed by gran- 

 ite : and hence I hesitate to impute the elevation of our plastic clay 

 to that rock, especially on such equivocal evidence as I now possess, 



Supposed evidence of Volcanic Agency at Gay Head. 



The opinion, I ought, however, to remark, has been advanced by 

 writers too respectable to be passed unnoticed, that there are traces 

 of volcanic action at Gay Head. The great quantity of lignite there 

 mixed with the clay, giving the whole mass an appearance somewhat 

 like cinders, and the ferruginous conglomerate, in which the pebbles 

 are coated over with the brown hydrate of iron, often exceedingly 

 resembling the conglomerated semi-fused mass that is raked out of a 

 furnace, would very naturally lead a person, unpractised in geology, 

 to refer them to volcanic agency. These are undoubtedly the sub- 

 stances intended by Dr. Baylies, when he speaks of "masses of char- 

 coal,'' and " large stones, whose surfaces were vitrified."! It is now 

 well understood, that neither lignite nor the hydrate of iron, require 

 heat for their production. 



Geological Speculations of the Aboriginees. 



Gay Head being naturally a place of resort for the Indians, they 

 could not but notice its peculiarities. And they had an advantage over 

 geologists of modern times in explaining phenomena. For when 

 a difficulty presented itself, they had only to call in the aid of some 



* Geological Transaction, Vol. 2. p. 161. 



t Transactions of the Amer. Acad, of Arts and Sciences, Vol. 2. part 1. p. 150. 



