282 DR. THOMAS STERRY HUNT ON THE « 
Feet. 
OMAurOralIIMEStOnes RE cece eeetee eee ee sere 
1. Upper Primal slates with sandstone layers... .... … 300 
2: Yellow Sandstone: = CRE de oeceeee eases eae ee 200 
35 Waminatedislaty bete Re eee 350 
4. Middle Primal sandstone, with Scolithus..............000+ , 50 
DU Lower! Primal slatesse..--recsese seats eeeee eee eee UD 
A section at Chikis, on the Susquehanna, also described by Rogers, gives a still greater 
thickness of strata referred by him to the Primal; the base of the series not being exposed. 
We have, as before, 
Feet. 
1 Wipper-Puimalés) Ales Renee eeaee eee 1800 
2: Wihitersandatome rene eee eee sto nee eee eee eee 27 
Bago) Cite een cay ane ened Sc? a nee Due a eo NE eee LE ee 300 
A= SAO STON Wilts COMUNUB Eee eee Re 
We shall notice further on the characters of the Lower Primal slates as seen elsewhere 
in their distribution, both in Pennsylvania and in other states. 
$37. Since the time when Rogers made his geological investigations in Pennsylvania, 
researches in various parts of the Atlantic belt, and elsewhere, have shown that between 
the ancient gneisses which were Enown to him, and the base of the Primal series, there are, 
in many localities, one or more groups of crystalline stratified rocks. Of these, portions of 
the Huronian, and of the younger gneisses and mica-schists which have been called Mont- 
alban, present certain mineralogical resemblances to the schists of the Lower Primal ; which, 
as well as those interstratified with and overlying the Auroral, are, as was stated by Rogers, 
more or less distinctly crystalline schists. Misled by these resemblances, Rogers confounded 
these crystalline Primal strata with portions of the groups lying between them and the 
older gneiss ; including both under the general name of “ semi-metamorphie schists.” 
§ 38. No stratigraphical break separates the NScolithus-sandstone from the Lower 
Primal slates, and thus the whole of these so-called semi-metamorphic schists below this 
horizon were included in one great group. This was described as a downward pro- 
longation of the Paleozoic series; but, from the absence of organic remains, was distin- 
guished alike from this, and from the more ancient or so-called Hypozoic gneisses, 
by the name of the Azoic series. There was, according to Rogers, among the rocks of the 
Atlantic belt, but “one physical break, or horizon of unconformity, throughout the immense 
succession of altered crystalline sedimentary strata,” namely, that at the summit of the 
ancient or Hypozoic gneiss ; and “ 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 of the Pennsylvania survey; that 
is to say, in the Primal white sandstone which, even where very vitreous, and abounding 
in crystalline mineral aggregations, contains its distinctive fossil, the Scolithus linearis.” 
§39. In the opinion of Rogers, the whole series of strata below the Levant sandstone, 
had, in the southeastern area, been the subject of alterations, which had given to them the 
characters of crystalline rocks. I have elsewhere set forth at some length the views of — 
Rogers_on this point, and have shown that his conclusions with regard to the so-called 

