212 0. S. Prosser — Upper Hamilton and 



position of an ideal rowlandite would appear as in the first 

 column below, while the second column shows the percentages 

 required to conform to the above formula. 



Calculated for 



Found. Si 4 Y 4 FeFl 2 14 . 



Si 12-73 12-93 



Y 50-83 50-37 



Fe 6-50 6-46 



Fl 4-05 4-39 



O 25-89 . 25-85 



100-00 100-00 



The agreement is very close and becomes much more so if 

 the suggested slight increase in silica and fluorine is allowed. 



Aet. XXXIII. — The Upper Hamilton and Portage Stages of 

 Central and Eastern New York ; by Chakles S. Prosser. 



The correlation of the Upper Devonian rocks of central 

 and eastern New York has for a long time been a question of 

 great difficulty and several interesting statements have recently 

 been published in reference to this problem. The region is 

 one familiar to me, and while recognizing the generally accu- 

 rate description of the geologic sequence of this mass of rocks, 

 the correlation and consequent age of a portion of the terranes 

 under consideration, included between the base of the Oneonta 

 sandstone and the top of the Hamilton stage, seem to call 

 for a brief explanation of their paleontology and stratigraphy. 

 This region was somewhat briefly described by Dr. H. S. 

 Williams in a paper on " The classification of the Upper 

 Devonian"* in 1885; in addition to this a large amount of 

 data has been accumulated in reference to the paleontology 

 and stratigraphy of the region, the greater part of which is in 

 the hands of Dr. Williams for use in the preparation of a 

 monograph describing the Devonian system of the United 

 States. 



The term " Oneonta group " has been used for two entirely 

 different geologic terranes in the same region of New York, 

 hence it would seem advisable to review the history pf the use 

 of the names under consideration. 



The Oneonta sandstone was defined by Yanuxem in 1840, as 

 follows : " Montrose sandstone, or sandstone of Oneonta ; this 

 is the last or upper rock of the third district [third geological 



*Proc. Am. Assoc. Adv. Sci., vol. xxxiv, p. 225. See in particular Sections No. 

 Y.III, IX, X on the chart of meridional sections accompanying the paper. 



