Igneous Origin of some Trap Rocks. 123 



last rock is also cut down for several yards ; far below the line, where 

 any peculiarity of appearance derived from the trap ceases. 



The general height* of this grand front is between forty and fifty 

 feet, sometimes falling short of the latter, and rarely if ever, exceeding 

 it. The trap rock is commonly from fifteen to thirty feet thick per- 

 pendicularly, and the section of the sandstone is from ten to fifteen 

 or eighteen. 



Both rocks, as thus cut through for nearly a mile, in this extensive 

 quarry, exhibit a magnificent section ; such as a geologist, wishing to 

 study the origin of the trap rocks, would be most anxious to see, but 

 would hardly expect to find. To others, the place is worth visiting 

 on account of the beauty of the scenery. In the retrospect towards 

 Hartford, is the grand and rich valley of the Connecticut — before 

 you, the vales of Newington and West Hartford, almost equally beau- 

 tiful ; and the view, in both directions, is bounded by hills and moun- 

 tains, which, to the north and south, appear interminable. 



But the geologist, withdrawing his eyes from the landscape, will 

 rivet them upon the junction of the trap with the sandstone ; whose 

 relative positions will he, at once understood, by inspecting the sec- 

 tion which forms the frontispiece of this number, and for which I am 

 indebted to the pencil of Mr. Daniel Wadsworth, who, with the Rev. 

 Dr. Wainwright, and other gentlemen, accompanied me to the spot. 

 It will be seen, in the print, that the trap, in some parts rudely col- 

 umnar, in others amorphous, reposes upon regular strata of the argil- 

 laceous sandstone ; just as a collection of pieces of hewn timber may 

 be supposed to stand, on end, and close together, upon a pile of boards 

 or planks. The portion of the rocky ridge represented in the pic- 

 ture is about eighty feet, in the horizontal direction ; the trap is there 

 twenty eight feet thick, and the sandstone that is cut through is six- 

 teen feet tliree inches, so that the whole height at that place does not 

 exceed forty five feet. The figures of men at the foot will afford a 

 palpable scale. The water in the hollow, is an accumulation from 

 rain, in the bottom of the quarry. 



This argillaceous sandstone has a few peculiarities which deserve 

 description. The flat surfaces where the strata join each other, are 

 glazed as if they were varnished, and they are marked by fluctuations, 

 like those produced in soft moveable mud or sand, by undulating wa- 

 ter ; and also by irregular fines, running about upon their surfaces, like 



* I speak of the depth of the excavation, not of the height of the ridge, above the 

 adjacent country, which is much greater. 



