412 A. C. LANE 



the water and much progress had been made toward the evolution 

 of the Devonian forms. Just as in New York higher and higher 

 horizons of the Eo-Devonian rest to the west on the Sahna and water 

 hme, so in Michigan to the southeast and south higher and higher 

 horizons of this formation rest on the Sylvania. It is also true that 

 the Corniferous or Dundee rests on various members of this. The 

 Corniferous (Onondaga) above is unquestioned Devonian. The 

 Monroe below the Sylvania will, by general consent, be classed with 

 the previous period. But the Sylvania has often been called Oriskany 

 and the fossils of beds above are remarkably like Hamilton forms, 

 while the very top of the Lucas dolomite has been generally taken to be 

 below the Devonian. 



If, with 'H. S. Williams, we place the base of the Devonian at the 

 Oriskany and class the Lower Helderberg beneath as Silurian (Onta- 

 rian) as used to be common (compare the 1892 edition of LeConte 

 with the latest) we can then surely place the whole Monroe with 

 the Silurian as I did. Canadian writers have generally grouped 

 the Sylvania as Oriskany. 



But beneath the Oriskany comes the Lower Helderberg series 

 of New York 300-400 feet^ and Pennsylvania 600 feet, and in Europe 

 stages E and F, and the relation of these to the faunas is a complex 

 problem of paleogeography. After the Salina (all up) was there a 

 see-saw — first the Michigan trough down (Upper Monroe), then up, 

 and the New York Helderberg down ? This is the view accepted 

 by Grabau. Or is it possible that at the time of the Sylvania the 

 Michigan basin was so separated from that of New York that the 

 two could have separate faunal developments at the same time, the 

 New York receiving precursors of the Corniferous, Michigan of 

 the Hamilton, while somewhere around there lingered relics of the 

 Silurian faunas which re-established themselves when the old anhy- 

 drite- and dolomite-forming conditions returned in Michigan ? This 

 would imply that on Schuchert's Plate 72 a long sound of Upper 

 Monroe should extend, opening to the north. 



On the whole, the greater break as well as the most widespread, 

 and therefore the one best fitted to mark the beginning of the Devon- 

 ian, seems to be that above the Detroit River series. For there 



I Schuchert, Sm//. G.S.A., XI (1900), 270; XX. 



