690 SCHUCHERT A:b^D TWENHOFEL ORDOVIClC-SILURIC SECTION 



locally shaly. At Clear Water Point the base of the Mingan series is not 

 well exposed, but the basal conglomerate appears to be absent imme- 

 diately above a zone 20 feet thick of yellowish gray limestone that is 

 here regarded as the top of the Eomaine series. Logan (Logan, 1863, 

 page 134) gives the thickness of these same beds as 28 feet, and it is 

 probable that he included in his estimate the higher 8 to 10 feet of strata 

 which the writers of the present paper will place at the bottom of the 

 Mingan. This series will then begin here with a gray, yellowish and 

 bluish fine grained, highly calcareous, thin-bedded sandstone 42 inches 

 in thickness, followed by 6 inches of green shale, 2 feet of calcareous 

 sandstone, and finally by 4 feet of green more or less nodular shale. 



On Harbor Island the conglomerate, which is here 3 feet 8 inches 

 thick, is followed by 4 feet of green arenaceous shale, 8 feet of shale and 

 shaly limestone, and about 3 feet of calcareous sandstone. 



The Mingan zones A^ and Ag are, therefore, seen to be very variable 

 in character in closely adjacent areas^ and this is especially true for the 

 higher zone. There is here the unmistakable physical evidence of a very 

 variable shore character, just such as would be expected at the margin of 

 an invading sea. 



Mingan formation, Zone A^. — The shale beds are followed by gray to 

 light greenish, more or less thin-bedded limestones that locally have more 

 or less thin zones of shale in the lower part. On Quarry Island this zone 

 is about 45 feet thick, the lower 10 feet of which are rich in fossils. On 

 the Parroquet group, about 30 feet of this zone are exposed when the sec- 

 tion passes beneath the sea. On Phantom Island the uppermost 15 to 20 

 feet are of this zone and represent the lower fossiliferous portion of 

 Quarry Island. The upper 50 feet of Harbor Island, with the possible 

 exception of the higher beds, are also of this horizon with the greatest 

 abundance of fossils in the lower portion. At Clear Water Point this 

 zone begins with the nodular fossiliferous limestone 10 feet thick, fol- 

 lowed by 25 feet of gray and brownish gray dense limestone. 



The fauna of the lower 10 to 15 feet of Mingan Ag zone may have 

 upwards of 60 species, among which the following are either the most 

 abundant in individuals, or are of described species, or forms thought to 

 be guide fossils to the horizon^^ (the species marked with a * occur in 

 the Chazy of Few York) : Eospongia roemeri, "^Zittelella varians, 

 *Strephochetus cf. ocellatus, Solenopora compacta var., Inocaulis n. sp., 

 "^Stylaroea pa^^va, Bolhoporites (very rare), ^Schizamhon dupUcimuratus, 

 Bythotrypa, Crepipora, Stictoporella cf. anguJaris, Rhinidictya mutahilis 



u For many of these identifications the authors are indebted to Dr. E. O. Ulrich and 

 Dr. Percy B. Raymond. 



