62 Savage emd Orooks — Early Silurian RocTt's of the 



tion. On the whole this fauna seems to be much more 

 closely allied to that of the Edgewood formation than to 

 any other. 



From the fossil lists given above it will be seen that 

 the species of fossils occurring in the Fiborn limestone 

 are quite similar to those in the Hendricks dolomite, but 

 in the former shells of ostracods and coralla of Favosites 

 forbesi var. are more numerous than in the latter. 



The Fiborn limestone facies appears to represent a 

 large lens of fine-grained limestone that appears to be 

 confined to northern Michigan. This well marked phase 

 has not been recognized farther west in Wisconsin, or 

 farther east in Ontario. It may be noted in the detailed 

 section that occasional layers of fine-grained, non-mag- 

 nesian limestone, similar to the Fiborn, also occur lower 

 down, in the Hendricks dolomite. The fauna of the 

 Fiborn limestone shows it to be closely allied to the 

 Hendricks dolomite, and it probably represents a local 

 facies of that formation. The fossils of the Manistique 

 series of Smith, which succeeds the Fiborn limestone, are 

 characteristic Niagaran species. 



The thickness of the Fiborn limestone varies from 

 place to place, but is not known to exceed 30 feet, and is 

 generally considerably less. The complete thickness of 

 the Hendricks dolomite is known in only a few places. 

 Logs of test borings in the vicinity of Hendricks quarry 

 show a thickness of 145 feet of this formation, and pos- 

 sibly a greater thickness may be found. The thickness 

 of this formation corresponds rather closely to that of 

 the Mayville limestone in Wisconsin, where an aggregate 

 thickness of 149 feet was penetrated in a boring on the 

 floor of a quarry south of Mayville. 2 



About one-half mile north of Hendricks quarry the 

 Fiborn limestone is exposed near the top of a bluff 90 

 feet high, but the underlying Hendricks dolomite is con- 

 cealed by a heavy talus. From numerous limestone 

 fragments in this vicinity moulds and casts of shells of 

 Virgiana barrandei var. mayvillensis were collected, and 

 the ledge from which they came is probably no great dis- 

 tance from this exposure. Three-fourths of a mile north 

 of the Blaney quarry of the White Marble Lime Com- 

 pany, two and three-fourths miles north of Blaney Junc- 

 tion, the Hendricks dolomite is exposed over an area a 



2 Savage, T. E., Bull. Geol. Soc. Am., vol. xxvii, p. 308. 



