THE FAUNAS AND THEIR RELATIONSHIPS 413 



Between horizon A-1 and A-2 there is an interval of 537 feet of lime- 

 stone, which appears to be completely unfossiliferous. 



Horizon A-2 is 937 feet above the base of the section. In it are found 

 great numbers of an Asaphoid trilobite and broken fragments of several 

 varieties of the genus Eccyliomphalus. The identifiable species are 

 AsapMis marginalis Hall, Riheiria calcifera Billings, R. parva sp. nov. ; a 

 spirally coiled Eccyliomphalus, similar in appearance to E. distans Bil- 

 lings, but smaller ; Ophileta uniangulata Hall. There are a number of 

 other species represented, especially of Eccyliomphalus, but in such a 

 fragmentary condition that trustworthy identification is difficult. The 

 fossils range through a vertical height of 90 feet ; the Asaphiis marginalis, 

 which is exceedingly abundant, though represented chiefly by pygidia, 

 occurs within the limits of a few feet at the base of the horizon in an 

 oolitic limestone. The Ribeirias are associated with the Asaphus. The 

 Eccyliomphalus occurs above these forms, chiefly at the top of the 

 horizon. The fauna shows decisively the Beekmantown age of this 

 second horizon. 



Immediately succeeding A-2 there are 1,499 feet of unfossiliferous 

 limestone before the third horizon, A-3, is reached, or 2,536 feet above the 

 base of the section. There is an abundant fauna present in horizon A-3, 

 ranging through 150 feet in vertical height. The principal fossils found 

 at this horizon are Bathyuras amplima.rginatus Billings, Maclurea affinis 

 Billings, Liospira strigata, sp. nov., Protoivarthia rossi, sp. nov., and Dal- 

 manella suhsequaia gibhosa (Billings). The genera and species of this 

 horizon are strikingly similar to those described by Billings from the 

 Calciferous of the Mingan islands, gulf of Saint Lawrence. So marked 

 is this resemblance of faunas that there can be little question that they 

 represent identical horizons. The Mingan Islands horizon has always 

 been regarded by the Canadian geologists as Upper Calciferous. This 

 view accords well with the fact that the Pennsylvania horizon is the 

 uppermost fossiliferous horizon found in the Beekmantown. Provis- 

 ion.ally at least, horizon A-3 may be referred to the Upper Beekmantown. 



All of this great series of limestones described above, with a thickness 

 of 4,803 feet, is to be regarded as Beekmantown. As already indicated, 

 it is possible to divide the formation into three divisions : a lower, char- 

 acterized by Ophileta complanata ; sl middle, msirkedhy Asaphus maj^ginalis^ 

 and an upper, distinguished chiefly by Bathyurus amplimarginatus. 



Horizon A-4 is separated from A-3 by 2,335 feet of unfossiliferous 

 dolomitic limestone. Some of the Pennsylvania geologists, notably 

 H. D. Rogers,* have referred to this intervening formation as a coralline 

 limestone in part. The writer has found but few traces of fossils in these 



* H. D. Rogers : Geol. of Pennsylvania, vol. i, part i, p. 471. 



