426 PROCEEDUirGS OF THE GEOLOGICAL SOCIETY. [May 10, 



IV. Lower Siltjeian (Si. John^ Geoitp). 



In my article on the geology of St. John county allusion "was made 

 to the discovery of TrUobites in the slates of the St. John group. A 

 collection of more perfect forms, made later in the same year, 

 together with those collected by our party last summer, were placed, 

 in the hands of Mr. C. F. Hartt for study and determination. By 

 means of these fossils he was enabled to fix with precision the geo- 

 logical horizon of the basal portion of this formation, and thus furnish 

 a datum-line by which the underlying formations and superior sedi- 

 ments have been approximately co-ordinated. 



A preliminary notice of these organisms will appear in Professor 

 Bailey's report, and descriptions of the species in a paper by Mr. Hartt, 

 which wiU form an appendix to the same. Of Trilobites there are four 

 genera, namely : — Paradoxides, 5 species, Conocephalites, 7 species, 

 Agnostus, 1 species, and a new genus (?) allied to Conocephalites, 1 

 species. There are also six species of Brachiopoda, of the genera 

 Orthisina, Discina, Obolella and Lingula. Mr. Hartt remarks that 

 aU these species are apparently new. 



Geographically the St. John series or formation occupies a narrow 

 valley, about thirty miles long and four miles wide, having Azoic 

 and Huronian rocks on the north-west, and limited on the south- 

 west by Huronian and Devonian .ridges, with a spur passing into a 

 valley which separates the former from the latter series. 



By the following section it will be seen that but a small part of 

 this formation is yet known to be of Primordial age : — 



feet. feet. 



1 . a. Grey sandstone or quartzite 50 



b. Coarse grey arenaceous shale. '\ 



[This and the preceding are passage-beds fi'om the 

 Coldbrook or Huronian group.] 



c. Grey argillaceous shale, rich in fossils : Paradoxides, 



Orthisina (?), Conocephalites, Obolella. V\bO 



d. Black carbonaceous shale, full of fossils : P«ra(fo«'(?cs, 



Conocephalites, Orthisina, Discina, Orthoceras, and i 

 a thin, subtriangular shell resembling Theca, all | 

 much distorted ) 200 



2. a. Dark-grey shales, with thin seams of grey sandstone. .220 "1 



b. Coarser grey shales, with grey flagstones 200 j- 550 



c. Grey sandstone and coarse shales : Lingula, &c 130 J 



3. a. Dark-grey shales, finely laminated 450 ^ 



b. Black carbonaceous and dark-grey argillaceous shales, l 750 

 more compact than the last 300 J 



4. Shales and flags resembling 2a &b 800 (?) 



5. Black carbonaceous shales, resembling 3 b, but finer and 



softer 4.50 



6. a. Shales and flags like 2 a & b: Lingula, a Conehifer, 



Coprolites, Worm-burrows, and Crustacean markings 700 (?) i 

 b. Grey and ferruginous sandstones and beds of coarse 1- 1100 (?) 



shale : Lingula 400 J 



7. Black carbonaceous shales, finely laminated 650 



4500 



[N.B. The thickness of 4 & 6 « is apparently much greater than tliis ; but 

 it is supposed that the beds are repeated by folding. Tliis may also be the case 

 with some of the other divisions.] 



