468 THE AZOIC SYSTEM AND ITS SUBDIVISIONS. 



tiveen the two groups of strata, and established, by ocular proof, the correct- 

 ness of the previous inductiony 



In accordance with this latter statement, and not with the former, we 

 do not find on the general geological map of the State accompanying 

 the Final Keport any indication of the two gi'oups in question. All the 

 crystalline rocks seem to be indicated by a single color, and included 

 under the term " hypozoic." 



Reading still farther in Professor Rogers's Report {I. c, p. 63), we are 

 even more surprised than before, when we learn that 



" 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 un- 

 conformity throughout the whole immense succession of altered crystalline 

 sedimentary strata, and within this region but one Palaeontological 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-fossil- 

 iferous or azoic deposits to those containing organic remains, lies within the 

 middle of the primal series or group of the Pennsylvania survey, that is to say, 

 in the primal white sandstone The Primal slates beneath the sand- 

 stone, antl in intimate alternation with it, possess not a vestige of organic life, 

 nor has any such been yet discovered anywhere within the limits of the Atlan- 

 tic Slope, or on the northern or western borders of the Great Appalachian 

 Basin of North America." 



Farther on in his Report, Professor Rogers remarks concerning his 

 two systems of rocks, — the Hypozoic or Gneissic, and the Azoic, — 

 that " the members of the two groups often simulate each other so 

 closely, and a/'e indeed so identical in mineral aspect and structure, as to 

 baffle all attempts at distinguishing them lit hologic ally." Again, we are 

 informed that these systems are nevertheless distinct from each other, 

 and "susceptible of delineation on the geological map." But, it is im- 

 mediately added, " the State geologist did not venture to define them 

 on the map." 



Before proceeding to notice the results attained by the Second Geo- 

 logical Survey of Pennsylvania, in connection with the investigation and 

 classification of the crystalline rocks of that State, it will be well to refer 

 to the views published by Dr. Hunt at various times between the com- 

 pletion of the First Survey and the beginning of the Second. This is 

 the more desirable, because he was employed by the State Geologist 

 (Professor Lesley) " to collate all the known, supposed, and suspected facts 

 of American Azoic Geology " for publication by that Survey, apparently 

 as a sort of manual or guide to the mysteries of that department of the 

 science, for the use of future investigators. Professor Lesley considers 



