153 Pfof. Rogers's Address before the 



of the lowest formation of the Appalachian system, while the semivitri- 

 fied quartz rock of the western part of the Hoosac mountains was stated 

 to be nothing else than the white sandstone (Potsdam sandstone) of the 

 same series slightly altered.* I am gratified to find from Prof Mather's 

 report, that these views of identity are embraced by him, as they now 

 are, if I mistake not, by Prof. Hitchcock. Prof Mather indeed says that 

 he has traced the slate (Hudson slate) through all its gradations into 

 talco-argillaceous and talcy slate, and into graphic and plumbaginous 

 slate, the limestone from compact sandy and slaty, to sparry, slaty 

 talcose, and crystalline limestone, within short distances, and the Pots- 

 dam sandstone, to a hard compact and granular quartz rock. It is true, 

 Prof. Emmons has presented in his report, a series of sections of the 

 strata exhibiting an unconformity at the passage of his Taconic into the 

 rocks of the Champlain division, but I must take the liberty of express- 

 ing my disbelief of the existence of any such unconformity, and of ob- 

 serving that in the prolongation southwestward of this altered and pli- 

 cated belt as far as the termination of the Blue Ridge in Georgia, a 

 distance of one thousand miles, no interruption of the general conformity 

 of the strata, has ever met the observations of my brother or myself. 



It would appear thus that the Potsdam sandstone forms the base of 

 the palseozoic strata in the latitude of Lake Champlain, or at least in 

 the region of the lake and of the Mohawk river. Is this formation then 

 the lowest limit of our Appalachian palseozoic masses generally, or is it 

 the system expanded downwards in other districts, by the introduction 

 beneath of other conformable sedimentary rocks } From the Susquehan- 

 na River southwestward, a much more complex series of strata comes 

 in below the bottom of the lowest limestone, than is any where seen north 

 east of the Schuylkill. In some portions of the Blue Ridge belt there 

 are at least four independent and often very thick deposits, constituting 

 one general group, in which the Potsdam, a white sandstone, is the 

 second in descending order. The uppermost of these is an arenaceous 

 and ferriferous slate, many hundred feet thick, in which the only fossil is 

 a peculiar fucoid. Beneath this lies the Potsdam sandstone, and under 

 this again a mass of coarse sandy slate and flaggy sandstone, amounting 

 sometimes to six hundred or seven hundred feet, below which occurs in 

 Virginia and east Tennessee a series of heterogeneous conglomerates. 

 Neither of the two lowest of these masses, has yet rewarded research 

 with a single fossil, and therefore the white or Potsdam sandstone is yet 



* See Proceedings of American Philosophical Society, Jan. 1 , 1841. 



