Februart 5, 1904.] 



SCIENCE. 



235 



survey of the Watkins Glen quadrangle pre- 

 paratory to forming the folio map of this 

 region. The results of the field work are now 

 sufficiently well elaborated to permit of the 

 following announcement : 



The general similarity of the rocks of this 

 whole region has made the use of paleontology 

 in classifying them a necessity, and the re- 

 sulting classification is primarily based upon 

 paleontological evidence. 



The rocks of the region have a general 

 southerly dip, and the formations exposed on 

 the surface are all Devonian. The lowest 

 formation mapped is the Genesee black shale 

 outcropping in the extreme northern part of 

 the quadrangle in the bottom of the valleys of 

 Cayuga and Seneca Lakes. Two major for- 

 mational divisional planes are traceable across 

 the quadrangle from east to west. These 

 planes separate the Genesee from the following 

 Portage, and the Portage from the succeed- 

 ing Chemung. The paleontology is the chief 

 ground for drawing these lines, but the lithol- 

 ogy is in harmon;^ with the other evidence. 

 The Portage formation lying between these 

 two planes attains a thickness of from 1,250 

 to 1,300 feet. Below it the Genesee is 120 

 to 150 feet thick. Above the Portage 1,225 

 feet of Chemung has been traced, but the top 

 of the range of the Chemung fauna was not 

 reached in the area surveyed. 



No other planes offered sufficient continuity 

 of evidence, either lithological or paleon- 

 tological, for drawing the lines across the 

 whole quadrangle. In the eastern half of the 

 quadrangle the Portage is divisible, on clear 

 paleontological evidence, into three members : 

 the lower Portage, approximately 250 feet; 

 the Ithaca, 400 feet; and the upper Portage, 

 600 feet thick. Paunally the same species 

 characterize the lower and upper members of 

 the Portage. The central member (the 

 Ithaca) holds an entirely distinct fauna, 

 homeotopic with that of the Hamilton and 

 Chemung faunas lying below and above it. 

 The lithological characters of the Ithaca are 

 in general distinct from those of the Portage, 

 but the difference is due rather to the domin- 

 ance of the argillaceous shales in the Ithaca, 

 over the flags and thin-bedded fissile, and 



generally dark-colored, shales which are more 

 characteristic of the Portage, than to any uni- 

 form lithological character of either. 



In the Seneca Lake valley the subdivision 

 of the Portage into three members can not 

 be made out sharply upon either lithologic 

 or paleontologic evidence. A few scattered 

 species of the Ithaca fauna appear within their 

 proper zone, but the lower and upper Portage 

 conditions dominate all through the sections 

 for the whole 1,200 to 1,300 feet. The Portage 

 fauna also recurs in some sections after the 

 entrance of the Chemung fauna into the gen- 

 eral region. ' The faunas of the Genesee and 

 Portage are more closely related to each other 

 biologically than either of them is to the 

 Hamilton or to the Chemung fauna. 



A recurrence of Hamilton species takes 

 place in several zones ; the more conspicuous 

 cases are near the base of the Ithaca member, 

 in Cascadilla Creek in Ithaca (as was stated in 

 Bulletin 3 of the U. S. Geological Survey in 

 1884) ; near the base of the Chemimg within 

 the lowermost 100 feet of several sections in 

 the quadrangle; and again in the upper 

 Chemung about 600 feet above its base. This 

 highest discovered Tropidoleptus zone is seen 

 in quite a number of the sections in the 

 southern half of the quadrangle. 



In these recurrent faunas the more char- 

 acteristic as well as dominant species are 

 Tropidoleptus carinatus, Rhipidomella vanu- 

 xemi, Cypricardella hellistriataj also Phacops 

 rana has been seen, and specimens of a Spirifer 

 not to be distinguished from typical Hamilton 

 forms of Spirifer (mucronatus) pennatus. 



The lower zone of this fauna in the Chem- 

 ung is below the first appearance of Spirifer 

 disjunctus, but the upper zone is hundreds of 

 feet above the first appearance of the typical 

 Spirifer disjunctus fauna, and in several sec- 

 tions that fauna occurs abundantly both below 

 and above it within a few feet of thickness 

 of strata. The recurrent species are generally 

 associated with a few of the common species 

 of the normal fauna of the part of ?ection in 

 which they occur, but Spirifer disjunctus has 

 not been discovered associated with them, 

 though often occurring below as well as above, 

 not very far distant. 



