RELATIVE AGE OP DETROIT RIVER SERIES 73 



The Flat Rock dolomite is not exposed at Amherstburg, unless the lowest beds 

 of the Amherstburg Stone Company's quarry belong to it; but the other divi- 

 sions are well shown. These are all more or less fossiliferous and at certain 

 places have yielded an abundant fauna. All divisions of the Detroit River 

 series contain Devonian faunal elements. This is most marked in the Am- 

 herstburg dolomite, and probably least in the Lucas dolomite. The Amherst- 

 burg dolomite is typically developed in the bottom of Detroit River at Amherst- 

 burg, Ontario, and within the last seven or eight years this has been excellently 

 exposed in the dry cut of the Livingston Channel. Near the north end of this 

 cut the rocks are very fossiliferous and nearly all of the abundant forms are 

 not only of marked Devonian aspect, but resemble decidedly the Onondaga 

 fauna. Some of the most striking resemblances are to be found among the 

 species of Cladopora, Cystiphyllum, Favosites, Hederella, Romingeria, Synapto- 

 phyllum, Syringopora, Crania, Meristella, Pentamerella, Productella, Reticu- 

 laria, Rhipidomella, Schizophoria, Spirifer, Stropheodonta, Conocardium, Mo- 

 diomorpha, Paracyclas, Schizodus, Bellerophon, Callonema, Eotomaria, Loxo- 

 nema, Platyceras, Tentaculites, Ryticeras, Dawsonoceras, Proetus, etcetera. 

 Such an aggregation of genera would alone be sufficient to demand comparison 

 with the Onondaga fauna, but in many cases even the similarity of the species 

 is so close as to have caused their identification with the Onondaga forms. 

 Certainly one can have no quarrel with the man who insists that this fauna 

 must be placed within the Devonian system. It is, in fact, a Devonian fauna. 

 But the massive layers of brown dolomite containing this fauna are overlain, 

 toward the south end of the cut, by similar beds carrying the Lucas fauna. A 

 close study of this latter fauna, which is the one that has usually been con- 

 sidered to have especially strong Silurian affinities, shows that it is different 

 from those to which it has been compared, and that the majority of its species, 

 that have been considered Silurian, were really described from the Lucas 

 dolomite of Michigan or from the Ohio outcrops of this same formation ; 34 

 per cent of the species listed by Grabau and Sherzer 4 are also found in undis- 

 puted Silurian deposits ; 9 per cent occur in typical lower Devonian, and 57 

 per cent are apparently not known outside of the Detroit River series. While 

 the Lucas fauna at first seems impossible as a Devonian aggregation, this 

 latter consideration decidedly minimizes the relationship to other known Si- 

 lurian faunas. 



In northwestern Ohio the Onondaga (Columbus) limestone rests uncon- 

 formably on the Lucas dolomite, but at Amherstburg and at the Sibley quarry, 

 nearly straight across the river in Michigan, it rests on the Anderdon lime- 

 stone. The dip of the rocks at the Amherstburg Stone Company's quarry is 

 to the west-southwest, although well records show that it evidently is reversed 

 at no great distance. A similar dip occurs at the Sibley quarry across the 

 river. In the dry cut of the Livingston Channel the dip is south at the rate 

 of about 100 feet per mile, thus seeming to indicate the rising axis of an anti- 

 cline of which the limbs slope away to east and west. This has led some men 

 to the belief that the Anderdon belongs immediately under the Onondaga, as 

 it has usually been found in surface outcrop. Also very serious doubt exists 

 in the minds of some as to whether there is a stratigraphic break or an erosion 

 surface at the top of the Anderdon limestone or between the Onondaga and 



* Mich. Geol. and Biol. Survey, Pub. 2, Geol. ser. 1, 1910, pp. 211-213. 



