248 



A series of gray and blue shales, containing nodules of blue lime- 

 stone, with fossils characteristic of the Calciferous Sandrock, was dis- 

 covered in August last by Mr. Billings, ten miles east of Phillips- 

 burgh, on the road to Freligsburgh, in Canada. Mr. Billings saw it 

 lying over the limestone that forms the following subdivision, but was 

 unable to make out its thickness, and its junction with the Black River 

 group, so that giving about one hundred and fifty feet for it is a mere 

 guess. 



The second subdivision in descending the series has been called by 

 Mr. Billings, in his interesting memoir, entitled. On some Rocks and 

 Fossils occurring near PhilUpshurgli^ Canada East — (see the Canadian 

 Geologist, August, 1861, p. 310, Montreal,) — ^Zwe, Thin-bedded and 

 Nodular Limestone. As Mr. Billings has given a good description of it, 

 I will not repeat it here. The fossils are very numerous one mile east 

 of PhilHpsburgh, and just behind the houses of the village of St. 

 Albans Bay. The most characteristic are, Camerella calcifera; Orthis; 

 Maclurea matutina ; Ophileta sordida, 0. levata, 0. complanata ; Eccu- 

 liomphalus Canadensis, E. intortus, E. spiralis; Pleurotomaria ; Mur- 

 chisonia ; Holopea ; Capulus ; Orthoceras ; Cyrtoceras ; Nautilus ; 

 Lituites imperator, L. Farnswortlii ; Bathyurus Sajfordi, B. Cordai ; 

 Amphion Salteri; Asaphus; Crinoids, Corals and Fucoids. 



Below this subdivision, and passing gradually into it without any well 

 defined line of separation, is a series of gray, almost white, limestone, 

 containing numerous veins of calc-spar, white marble, and magnesian 

 limestone. Mr. Billings has called it Magnesian limestone, but as true 

 dolomite is found in lar^e c[uantities in the middle of the Potsdam 

 Sandstone group, I think this name will have to be changed. The 

 fossils are rare in this lower subdivision, but Dr. G. M. Hall has found 

 in it some Cephalopods and Gasteropods half a mile south-east of Phil- 

 Hpsburgh. This last subdivision was very plastic when first deposited, 

 for it re-covers in discordant stratification the slates, and sometimes 

 also the Potsdam Sandstone of the Taconic system, and follows all the 

 accidents of the Taconic strata, as though they were covered with a 

 sheet of paste or plastic clay. I regard it as the bottom rocks of the 

 Silurian system in North America, containing the second fauna of 

 Barrande. It can be observed at PhilHpsburgh, on the shore line, east 

 of Swanton, and north of St. Albans Bay. It maybe that it forms the 

 marble of Middlebury and Rutland, but I am unable to speak with any 

 certainty, as it requires a special investigation, which I have been 

 unable to make. 



The Calciferous Sandstone always Hes in discordance of stratifica- 

 tion on the different groups of the Upper Taconic Strata ; sometimes 

 the discordance is 40°, generally 15° to 20°, and the direction of the 

 tetes de couches, or strike, as it is called in EngHsh, cuts always the 

 direction of the Taconic strata, at an average angle of 25°. 



