696 PROCEEDINGS OF THE BALTIMORE MEETING 



It is clear, however, that the true Hamilton fauna is not present in the York 

 River beds, because most of the diagnostic brachiopods are absent, even Tropi- 

 doleptus carinatus. From the character of the Hamilton faunas of -Maryland, 

 as described by Professor Swartz, I conclude that they came into this region 

 from the east, and if this is so, then all the more should the typical Hamilton 

 fauna be in the York River beds, if the horizon is of Hamilton time ; but it is 

 not there. That this Hamilton fauna was in existence elsewhere long before it 

 appeared in the United States is seen in the western European Coblenzian 

 faunas, and any one must be so impressed on looking at the photograph of a 

 fine Upper Coblenzian slab figured in Freeh's Lethaea Geognostica, plate 24&. 

 The problem before us is certainly a difficult one. 



1. I think Professor Williams takes too broad a view of the Saint Helens 

 fauna. The Hamilton-like fossils are in the agglomerates, and are not asso- 

 ciated with the limestone below the agglomerate that seemingly are in place. 

 Those that I collected are rather of Onondaga time than of Hamilton. 



2. I do not believe in Professor Williams's principles referred to on page — . 

 We can not in most cases rely on the common dominant species as the true 

 guides for time indicators. It is rather the rarer species. It is this principle 

 of Professor Williams that so many of us object to and which we believe 

 obscures the true chronological significance of the fossils. 



3. I do not hold with Doctor Clarke that the Pelecypoda of the Gaspe sand- 

 stone (York River zone of Williams) are of decided value in indicating Hamil- 

 ton time. They may just as well be of Coblenzian time (= Oriskany). 



4. The list cited by Williams is certainly striking as of late Lower Devonian 

 time, and more value should, it seems to me, be placed on these than the other 

 fossils of Hamilton aspect. 



As the true Oriskany assemblage, however, lies so far beneath — in fact, be- 

 neath the Grande Greve limestone — is what leads me to conclude that the York 

 River horizon holds a time above the New York Oriskany. According to my 

 observation, I am disposed to place this horizon definitely in the Onondaga. 

 If Professor Williams thinks it should go near the base of this horizon 

 (== Schoharie) I will not object, nor will I object if Doctor Clarke places the 

 time late in Onondaga, but I would not like to correlate the fauna with the 

 Marcellus. 



5. My paleogeographic maps are in harmony with the views here expressed. 



6. The true Oriskany is North Atlantic. The Camden chert of Tennessee 

 and Illinois has some of this Hamilton fauna. This is in agreement with 

 faunas of Msecuro and Erere. The home of this fauna is South American and 

 the southern Atlantic, and it occurs there as early as Oriskanian time. 



7. The Helderberg fauna is of the medial Atlantic. It comes in from the 

 Gulf, and probably also by way of New Jersey. In the Acadian region the 

 faunas are different, with only a few of the medial or southern Atlantic species. 

 Further, this element is unknown in northern Europe, but is widely known in 

 the Mediterranean extensions. 



REMARKS BY JOHN M. CLARKE 



The point of view taken by Professor Williams impresses me as a very nat- 

 ural one in view of the presence in the Gaspe sandstone fauna of certain lead- 

 ing Lower Devonic species, and this view was indeed that entertained by myself 



