Claypole.] '^O^ [Oct. 20, 



because the iron ore bed wliich overlies tlie red fucoidal bed has been (as 

 shown in the note above alluded to) confounded with another, occurring 

 several hundred feet lower down in the series. If the presence of Calskill 

 rocks is quite impossible with 100 feet of the Chemung missing, it would 

 be much farther from possible if 400 or 500 feet were missing, as supposed 

 in the report on Bradford and Tioga counties, p. 36. 



E, — 0)1 tJie Equivalent of the SclioJuirie Grit of New York in Middle Penn- 

 sylvania. 



The evidence of a single species, however "characteristic" it may be of 

 a stratum or gi'oup of strata in one place in favor of identifying that stra- 

 tum or group with another at any considerable distance, must always be 

 of little weight unless strongly corroborated by collateral evidence. Even 

 a single species, however, may be allowed to possess considerable value, 

 if thus corroborated. From this point of view the following note may pos- 

 sess interest: 



The Cauda- Gain or Schoharie g\i\s o^ New York overlie the Oriskany 

 sandstone. Of the former, Prof. Hall wrote in 18G7 (Pal. of N. Y., Vol. 

 4, p. 1): 



"The Cauda- Galli grit is almost a non-fossiliferous rock; a few fragments 

 of plant-like fossils and the peculiar surface-markings of the slaty lamina^ 

 from which its name is derived, being the only objects resembling organic 

 bodies which have fallen under my observation. A single specimen of 

 Platyceras, similar to P. tortuosum of the Oriskany sandstone, has been 

 found in this rock, * * * * It passes by almost imperceptible grada- 

 tions to the Schoharie grit, which is marked by the presence of numer- 

 ous fossils. The upper beds of the Cauda Galli grit, and also the lower 

 beds of the Schoharie grit preserve those peculiar markings which have 

 been termed Fucoides Cauda- Galli (Spirophyto)i Cauda- Galli)." 



It thus appears that these two strata in New York form really one group 

 within which no line of demarcation can be drawn. This group consists 

 of unfossiliferous beds at the base, Cauda- Galli beds above them, and fos- 

 siliferous beds at the top. 



The Cauda- Galli grit is, however, a stratum of very limited extent, con- 

 sidered lithologically . It does not occur in the western part of New York, 

 but is well marked in the east and extends into New Jersey. It thickens 

 toward the Hudson and reaches 50 or 60 feet in the Helderberg mountains. 



The Schoharie grit is distributed over almost the same area as tliat of the 

 Cauda- Gain grit, being specially well marked at Schoharie and in the Hel- 

 derberg. Both strata doubtless owe their deposition to the same set of 

 geological causes. f 



Neither of these grits occurs in Middle Pennsylvania in anj^ spot Avhich 

 has fallen under my observation. The strata immediately overlying the 

 Oriskany sandstone, in Perry and adjoining counties, consist of calcare- 



