Maryland Geological Survey 39 



divided into the Oriskanv and Corniferous periods, and the Catskill 

 peiiod having disappeared because it is not regarded as a distinct time 

 division but as synchronous with a varying portion of the Chemung period 

 and its later deposits perhaps formed in Carboniferous time. In Dana's 

 last summary of the Devonian, the OrisTcany period was composed of the 

 Oriskany sandstone; the Corniferous of the Schoharie and Corniferous 

 epochs; the Hamilton of the Marcellus and Hamilton epochs and tlie 

 Clumung period of the Portage and Chemung epochs, thus in general the 

 name of the epoch corresponding to the best characterized or most widely 

 distributed formation was selected as the name of the period. The de- 

 servedly commanding position in American geology held l)y Dana's 

 Manual for more than the last quarter of a century has made this 

 classification familiar to all students of oi;r geology. It will be remem- 

 bered, however, that the names used by the New York geologists were 

 for " groups " which usually had the rank of what are now called stages 

 or formations and that they were not applied to divisions of higher order. 

 The use by Dana of the same names for chronologic divisions of higher 

 rank introduced an element of confusion into the classification so that, for 

 example, when the term Hamilton is used it is necessary to state whether 

 it is an epoch or period in the chronologic sense, or a stage or group in the 

 stratigraphic sense. This double use of the same term led to embarrass- 

 ment in the correlation of the formations of other states with those of 

 New York and in recent years there has been a tendency among some 

 geologists to ignore to an unwarranted extent tlie New York names and 

 in their work in neighboring states to propose new names for formations 

 which agreed essentially with those of New York. 



Dr. Wm. B. Clark, Mr. Bailey Willis, and a few other geologists, how- 

 ever, had insisted that the formation or stage name ought not to be used 

 as the name of the division of next higher rank. This criticism has been 

 recognized as just by Dr. John ]\I. Clarke, the New York State Geologist 

 and Paleontologist. After discussing this question in their joint paper 

 Clarke and Schuehert have said, " The point has doubtless been reached 

 when these terms [Hamilton, etc. in the larger sense] representing though 

 they do important divisions of time and sedimentation, must give way to 



