Remarhs on the TaconiG System. • 281 



rocks upon its eastern shores. The first abrasion of the primi- 

 tive wonld yield breccias and conglomerates, arenaceous beds 

 would follow; these were succeeded by still finer argillaceous 

 deposits, since hardened into slates ; limestones followed, which 

 have been metamorphosed into marbles. 



These were repeated, the one upon and following the other, 

 until the whole series was completed. 



This simple statement of the structural geology brings us to 

 the third argument, — the thickness of the strata composing this 

 system. 



The limestones on the east, we have been able approximately 

 to measure. One thousand feet is the thickness in its present 

 dilapidated condition, in the valley of the Konkeput, and we 

 have good reason to infer that it once was more than 2000 

 feet thick. The raagnesian slates are fully 15,000 feet in thick- 

 ness. The limestones that followed were 1 to 600 feet thick ; 

 and the true Taconic slates of the state line of Columbia and 

 Berkshire are full five miles thick. The roofing and other 

 slates of Columbia Co. were three to three and a half miles in 

 thickness. 



In all, eleven to thirteen miles would be the maximum thick- 

 ness ; but allowing for any reduplication of the strata, or even 

 a folding of the same, the minimum thickness cannot be less 

 than five and one half miles, — a thickness much greater than 

 the Silurian, Devonian, and Carboniferous, which succeed this 

 eldest born of the sedimentary rocks. 



Our last argument is the unconformability and superposition 

 of the Silurian witli the Taconic. 



At Becraft Mt, Claurach, Kinderhook, and Ghent, in Colum- 

 bia Co., at Greenoble and Universit}'' Hill, in Rensellaer,. at 

 Bald Mt. and Mt. Toby, in Washington Co., and numerous 

 other localities might be cited, where the Taconic has its usual 

 steep inclination eastward, the lower Silurian either reclines 

 horizontally upon the upturned edges, or in troughs worn in the 

 slates, but in either case the superposition is manifest and 

 unmistakable. 



