252 bulletin: musel'm of comparative zoology. 



It is onlv some twentv years since it became known that there is in 

 the United States more than one kind of "Trenton." Naturally, 

 the history of the attempts to correlate the various kinds of " Trenton " 

 has been made in that time. The most troublesome of the still 

 unsolved problems is the exact relation of the "Trenton" (Rysedorph, 

 Chambersburg, Quebec City, Chickamauga, Sevier, etc.) of the Appa- 

 lachians to the "Trenton" (typical Trenton of New York, Trenton of 

 Ontario, Minnesota, etc.) of the interior. 



The Appalachian Trenton, if I may so call it, extends from the 

 destroyed end of the range at Gaspe in intermittent aligned exposures 

 as far as Georgia. A beginning on the description of its fauna was 

 made by Ruedemann (114) in his paper on the fossils in the pebbles of 

 the Rysedorph conglomerate, but practically nothing more has been 

 done along that line. Until the fauna is described the problem will 

 remain unsolved. We have, however, some inkling of what the fauna 

 is like, and notice that while in general similar to the Trenton faunas 

 of the interior, it differs in containing Echinosphaerites, Christiania, 

 Xidulites, Tretaspis, and Lonchodomas in abundance, these genera 

 being unknown in the interior Trenton. Many undescribed forms are 

 also peculiar to this Appalachian area, but the above familiar genera 

 are sufficiently striking. An entering wedge in the solution of the 

 problem has been driven home by the demonstration that the principal 

 zone of Echinosphaerites is, over wide areas, resting upon the Leray- 

 Black River. Here there is then a point of contact between the 

 Appalachian and interior provinces. Dr. Ulrich will agree to this, 

 but will include practically all of the limestone at Chambersburg, 

 for instance, with the Xidulites, Christiania, and Upper Echinosphae- 

 rites zones, in the Black River. To show that they represent the 

 Trenton is a difficult, perhaps at present, impossible task, but I shall 

 endeavor to present my reasons for so regarding them. To do this, 

 I must start with the section in New York and proceed by a round- 

 about western route to reach eastern Pennyslvania. 



Trenton in New York. 



The type-locality is in New York State, at Trenton Falls. The 

 section at Trenton Falls is unsatisfactory, in that the formation is 

 not there exposed to a low enough level to show the formation upon 

 which the Trenton rests. But a few miles east of Trenton Falls, at 

 Rathbone Brook, is another section which supplements the one at 



