564 president's address. 



the Trenton Limestone (Lower Silurian) of Canada. This is 

 associated with remains of Orthis and with annelid tracks. Mr. 

 Johnston, following the classification adopted at that time, refers 

 Lic7'ophycus to the algce, but recent observations of course prove 

 that it was probably merely the casts of worm burrows, with 

 radiating trails. 



The upper group consists of quartzose sandstones, conglome- 

 rates, limestones, slates, and grits. 



The limestones are largely formed of corals, including the widely 

 distributed genera Halysites, Favosites, Syringopo7'a,Phillipsastrcea, 

 &c. ; but these have not yet been specifically described. 



The earliest recorded cephalopods from Tasmania and Australia 

 belong to the horizon of the Gordon River Limestone, in which 

 they occur in some abundance, e.g. — Lituites Gouldii, Salter ; 

 Orthoceras antilope, Salter ; 0. Murchisoni^ Salter ; 0. theca, 

 Salter ; 0. Yonngii, Salter. No less than eight species of the 

 lamellibranch Cyrtodonta and two of Tellinomya have been 

 described by Mr. Salter (MS.),* and Mr, Johnston records 

 thirteen species of gastropods, including the characteristic Lower 

 Silurian genus Rajjhistoma. Raphistoma in Europe ranges up to 

 the middle of the Upper Silurian, but is more characteristic of 

 the Lower Silurian. Three genera of brachiopods, Orthis sp., 

 Retzia mima, Salter, and Rhynchonella sp., are also mentioned by 

 Mr. Johnston as occurring in these rocks, and also an undescribed 

 calcareous sponge (?), occurring in the Gordon Limestone. f 



The Sandstones of the Tasmanian Lower Silurian rocks are 

 finely laminated and ripple-marked. | With regard to the condi- 

 tions under which these rocks were formed Mr. Johnston states § : 

 "The laminated slates, with their graptolites, testify of fine muddy 

 sediments formed in the deep sea bottoms far removed from the 

 disturbing action of the surface waves ; the limestones composed 

 of corals and crinoids tell of quiet intermediate depths, where 



* f. Johnston, loc. cit. p. 63. 



+ Loc. cit. pi. II. fig. 13. 



X f. Johnston, loc. cit. p. 44. 



§ Loc. cit. p. 44. 



