34 



NEW YORK STATE MUSEUM 



finds the Square Lake limestone which he correlates by its fos- 

 sils with the Helderberg formation of New York and above it 

 the Chapman sandstone in which he finds forms representative 

 of the Silurian Tilestone fauna of Great Britain. From this he 

 argues that, inasmuch as these Silurian fossils occur in a forma- 

 tion more recent than the Helderberg limestone, the latter 

 should be regarded as Silurian. 



So far as the writer understands from the literature to which 

 he has access, the authors referred to, do not dispute each 

 other's identifications of fossils. The question then seems to 

 hang on the definition of a system; Dr Clarke holding that the 

 system begins where its faunas first appear, while Prof. Will- 

 iams holds that a system continues as far as its faunas linger, 

 the definition of a system having, apparently, not been pre- 

 viously fixed. The question would, therefore, seem to remain 

 open till the majority of geologists take the one side or the 

 other. 



On inquiring the opinion of the director of the United States 

 Geological Survey, he expressed the view that the matter was 

 still unsettled and so it is left by the present writer, the Helder- 

 berg being for the purposes of the present map classified in the 

 Silurian system according to the arrangement adopted by Prof. 

 Hall in the geologic map of 1894. 



The classification of Oneonta, Ithaca and Portage formations 

 as given on the map is based on a paper by Dr John M. Clarke 

 in the loth annual report of the state geologist, in which these 

 formations, though regarded as essentially of equal age, lying 

 between Hamilton and Chemung, are treated as separate 

 groups. In the classification printed by Dr Clarke in Memoir 

 3 of the New York State Museum, he proposes to give the name 

 of Portage group to the aggregate of the three formations and 

 use the term Naples for the formation designated in the pre- 

 vious paper as the Portage group. 



The following table shows the progress made in the term- 

 inology and classification of the rocks of Xew Y^ork since the 

 beginning of geologic study within its area. 



