GUELPH FAUNA IN THE STATE OF NEW YORK 21 



i The Barton beds (Spencer). Summit formation, 

 mostly dark dolomite with interbedded shale and 

 soft hydraulic layers, the latter considerably 

 employed in the manufacture of cement - - 87 feet 



2 Magnesian silicious beds filled with irregular 



nodules of light or white chert - 



3 Blue dolomite 



4 Rochester shale ------ 



For our immediate use we need not carry the section further down, 

 though the outcrop of the cuesta extends well into the Medina, as on the 

 Niagara river. To return to 1 : these heterogeneous strata, consisting of 

 shales, soft waterlimes and hard dolomites (Barton beds 1 ) contain discrete 

 faunas. In the hydraulic layers are Atrypa reticularis, Entero- 

 lasma caliculus, while the dark dolomites bear a distinct association. 

 With the aid of Colonel Grant and by the study of his collection and that 

 of the Hamilton Scientific Association, we are able to cite these as charac- 

 teristic species : Orthothetes subplanus, Leptaena rhomboi- 

 dalis, Orthoceras bartonense Spencer, a Dawsonoceras identical 

 with D. annulatum. More important however are the following, each 

 of which has been seen by Colonel Grant in but a single specimen : P 1 e u- 

 rotomaria perlata,* Coelidium macrospira, Trochoceras like 

 T. waldronense from the Waldron. The first two of these are 

 of distinctively Guelph character, and P. per lata has not been found 

 outside of that fauna. Colonel Grant finds that the upper layer of these 

 Barton beds, whenever stripped of soil, is everywhere deeply scored 

 by glacial shearing and believes that some part of the dolomites has 

 been thus carried away. Hence we get in these Barton beds, a clue 

 to or suggestion of the true Guelph fauna, which we may well believe 



'The employment of this term, so well known and long established in the English 

 Tertiary nomenclature, recalls how nearly Professor Hall came to duplicating the same 

 English nomenclature by introducing the terms Gait and Ludlowville. 



a It is apparently this species that has been described by Spencer as P. clipeiformis 

 from this upper horizon at Hamilton. [Univ. Mo. Bui 1. 1884. p. 57, pi. 7, fig. 6] 



