Maryland Geological Sukvey 111 



to differences iii food supply. These two factors were uiulouhtedly as po- 

 tent in their influence on marine life duriii,i;- ^liddlc Devonian time as they 

 are to-day. In most seas, however, the bathymetric principle is also a 

 factor in governing the abundance and variety of marine life ; this prin- 

 ciple is conspicuously operative in going seaward from a coast line and is 

 ail important factor in determijiing the off-shore and more pelagic pecu- 

 liarities of a fauna. With regard to the influence of depth or the bathy- 

 metric factor on a fauna the concise statement of Goodwin-Austin is well 

 worth quoting here. He writes: "The sublittoral zone of every sea and 

 ocean presents the fullness of its fauna and from that it decreases pro- 

 gressively and rapidly.''' If we bear in mind the possibility, or rather 

 the certainty, of ju'ovincial features or differences of very pronounced 

 charaeter appearing in the same fauna whenever marked changes arise 

 in the character of the sedimentation, food supply, or depth it will be 

 easy to understand why the fauna which will be described in succeeding 

 pages differs in some important details from the Onondaga fauna as it 

 is found in New York. The Tully limestone fauna of New York affords 

 an excellent Devonian example of the change in the character of a fauna 

 with change in type of sediment. 



This limestone which lies between the Genesee and Hand Hon Tornia- 

 tions covers a considerable area in central New York but thins toward 

 the east and toward the west of the region of its maximum development 

 and ultimately disajipears as a recognizable formation both in eastern 

 and western New York. Pressor " has shown that at the Tully horizon 

 in eastern New York after the limestone has disappeared only one or two 

 of the characteristic Tally fossils persist, the associated fauna represent- 

 ing the Hamilton congeries of the region. In western New York a band 

 of pyrites 1 to 4 inches in thickness represents the 20 inches of Tully 

 limestone in New York. The very interesting fauna representing the 

 western extension of the Tidly horizon has been described by J. ^M. Clarke 

 and T. B. Loomis. One of these authors states : 



"The Tully pyrite contains a fauna so diminutive that it escapes ordi- 

 nary observation ; so simple that it seems like a group of young forms ; and 



'■ Natural History of the European Seas, 1859, p. 246. 



= Fifteenth Ann. Rep. State Geol., New York, 1897, pp. 183-185. 



