302 ANNUAL OF SCIENTIFIC DISCOVERT. 



crystalline talcoid slates, and vitreous sandstones of the Chester and Mont- 

 gomery Valley, had been clearly demonstrated by the State geologist, 

 through a comparison of the strata with their corresponding formations in 

 a less altered condition further north ; but it was not until the resumption of 

 field research, upon the revival of the survey in 1851, that any distinctive 

 fossils were detected in these greatly changed rocks, which even in their 

 original state seem to have been almost destitute of their usual organic 

 remains. 



Assembling all the evidence which we now possess, we have in the Atlan- 

 tic slope by actual demonstration but one physical break or horizon of 

 unconformity throughout the whole immense succession of altered crystal- 

 line, sedimentary stratra, and within this region but one paleontological 

 horizon, that, namely, of the already-discovered dawn of life among the 

 American strata. This latter plane or limit, marking the transition from 

 the non-fossiliferous or azoic deposits to those containing organic remains, 

 lies within the middle of the primal series or group of the Pennsylvania 

 Surve} 7 , that is to say, in the Primal White Sandstone, which even where 

 very vitreous, and abounding in crystalline mineral segregations, contains 

 its distinctive fossil, the Scolithus linearis. The primal slates beneath the 

 sandstone, and in immediate alternation with it, possess not a vestige of 

 organic life, nor has any such been discovered anywhere within the limits of 

 the Atlantic slope, or on the northern or western borders of the great Appa- 

 lachian basin of Xorth America, either in this lower primal state, or in the 

 other semi-metamorphic grits and schists physically conformable with it, 

 and into which the true Paleozoia sequence of our formations physically 

 extends downward. We have thus, then, two main horizons, subdividing 

 the more or less metamorphic strata of the Atlantic slope into three systems 

 or groups; the one, a physical break or interruption in the original deposi- 

 tion of the masses ; the other, a life-limit or plane, denoting the first advent, 

 so far as is yet discovered, of organic beings. As these two planes are not 

 coincident, but include between them a thick group of sedimentary rocks, 

 separated from the lower physically, from the upper ontologically, we are 

 fully authorized, in the existing state of research, to employ a classification, 

 which recognizes a threefold division of all these lower rocks. To the most 

 ancient or lowest group, it is proposed to continue the name of gneiss, pre- 

 ferring, however, to call this division generically the GNEISSIC SERIES, 

 employing sometimes the technical synonyme Hypozoic, proposed by Pro- 

 fessor John Phillips, for these lowest of the metamorphic strata. To the 

 great middle group, less crystalline than the gneissic, and yet destitute of 

 fossils, the descriptive terms scmi-metamorphic or Azoic are applicable. 

 And to the third uppermost system, or entire succession of the American 

 Appalachian strata from the primal, containing the earliest traces of life, to 

 the latest true coral rocks, or last deposits of the Appalachian sea, it is here 

 proposed to affix, as for many years past, the well-chosen title, conferred 

 on corresponding formations in Europe, of the Paleozoic, or ancient life- 

 entombing system or series. Thus we have the Hypozoic rocks, or those 

 underneath any life-bearing strata; Azoic, or those destitute of any discovered 

 relics of life; and Paleozoic, or those entombing the remains of the earth's 

 most ancient extinct forms of once living beings. 



The Atlantic slope of Pennsylvania includes all these three systems of 

 strata. Where the azoic strata display their maximum amount of crystalline 

 structure or metamorphism, they often simulate the true ancient hypozoie 



