Mauyland Geological Survey 95 



into such an association, and hence are entitled to peculiar weight in 

 correlation. Although this conclusion may be uncertain, especially when, 

 as in the present case, the sediments of the beds to be correlated are like 

 those of the later and unlike those of the earlier formation, nevertheless 

 it is believed that particular weight should be given to the species found 

 elsewhere in later formations, as has been done in the reference of the 

 Helderberg to the Devonian and the Eichmond to the Silurian. If, on the 

 contrary, it is assumed that the zone of Liorhynchus Umitare represents 

 approximately the same interval in New York and Maryland, then these 

 beds are older than much of the Marcellus of New York and are syn- 

 chronous, at least in part, with the Onondaga. This view, which is that 

 of Kindle, is favored not only by the position of the beds below the Mar- 

 cellus of Mar^'land, IjTit also by the presence in them of so many species 

 that are restricted to the Onondaga in New York, including such plastic 

 forms as trilobites. 



When tlie emphasis of certain elements of the fauna leads to divergent 

 results particular weight may be attached to the relations of the fauna as 

 a whole. This criterion indicates again a close relationship of the beds 

 to the Marcellus, since it has been shown that over 60 per cent of the 

 significant species occurring in them are restricted to the Marcelllus and 

 later formations of New York. The entire argument leads to the con- 

 clusion that the beds are of early Marcellus age and also in part contem- 

 poraneous with the Onondaga. 



The explanation of these facts may perhaps be found in the conditions 

 shown to exist in New York, where the upper beds of the Onondaga are 

 of the same age as the lower beds of the Marcellus, and hence their faunas 

 are contemporaneous. In other words the beds under discussion may have 

 been deposited when both the Onondaga and Marcellus faunas were co- 

 existent in this area, a condition which would fully explain the mingling 

 of the faunas in the same beds and especially the presence of such highly 

 significant species as the Onondaga trilobites and the Marcellus goniatites. 

 Thus while tlie limestones of the Onondaga were accumulating off-shore 

 in New York dark shales were being deposited on ;;hore in the Appa- 



