440 PROCEEDINGS OF THE ACADEMY OF [Aug., 



OBSERVATIONS 05 THE STRUCTURE OF SOME CORAL BEDS IN THE 



HAMILTON SHALE. 



BY BURNETT SMITH. 



In the majority of the Paleozoic systems layers of rock occasionally 

 occur which are made up in large part of the remains of corals. 

 These coral masses in the attitudes and in the mutual crowding of 

 their individuals, as well as in their general field relations, exhibit 

 conclusive evidence that they lie in the position of original growth. 

 From certainly the Silurian upward we find among such coral layers 

 many which in structure approach, to a greater or less degree, the 

 reefs of existing seas. Such fossil reefs are, as might be expected, 

 more abundant in the limestones, and probably the Silurian and 

 Devonian rocks of this type furnish us with the best examples which 

 are to be found throughout the North American Paleozoic series. 1 

 In most cases, however, the reefs can be studied for only a small 

 part of their extent. For instance, the Onondaga limestone of 

 New York State is in many localities and through much of its thick- 

 ness nothing more than an old reef, but here, as a rule, only a small 

 horizontal section is exposed and the delimiting of the actual margins 

 of the coral masses must be left to the field of conjecture. In the 

 later Hamilton shale of the same region corals are a rather incon- 

 spicuous element when compared with the rich fauna of brachiopods 

 and mollusks. Locally, however, we find in the shales layers which 

 are composed of corals to the practical exclusion of other forms of 

 ife. Such layers are, in the main, of small thickness, and in studying 

 them we are again confronted with the usual limited horizontal 

 exposure. The coral reefs (if they can be dignified with the term) 

 which form the basis for this description are an exception in this 

 hot respect, for they present a large and very beautiful exposure of 

 about a mile along the eastern shore of Skaneateles Lake, in Onon- 

 daga County, New York. 



For purposes of convenience in presentation it is advisable to 

 consider these structures under the following headings: (1) The 



Chamberlin, in Geology of Wisconsin, vol. I, 1873-79; C. J. Sarle, 

 ncan Geologist, November, 1901, pp. 282-299 (chiefly Bryozoa), and 

 A. W. Grabau, in Bull. Geol. Soc. Am., vol. 14, p. 337 1903-4 



