FROM THE SILURIAN EOEMATION OF CANADA. 



259 



minute quartz crystals, uninjured and unworn, are washed into the 

 sea to constitute afresh the mineral sediments of the earth's crust. 



Mhombohedra of Magnesite. — These were left on the solution of 

 the limestones in dilute hydrochloric acid, the majority of them 

 occurring in a free and separate state, hut a few imbedded in small 

 fragments of chert, just like those figured by Professor Renard in his 

 memoir on the 4 Phthanites du Calcaire Carbonifere de Belgique ' 

 (Bull, de l'Acad. Roy. de Belgique, 2 me ser. t. xlvi. p. 471, 1878). To 

 determine their nature, as well as that of the rest of the limestone, 

 I made a preliminary qualitative analysis, first of the solution pro- 

 duced by the action of hydrochloric acid, and next of the undis- 

 solved residue. The former contained lime and magnesia, carbo- 

 nate of lime and phosphate of magnesia being precipitated in appa- 

 rently equal bulk ; the residue was boiled with strong hydrochloric 

 acid, and the resulting solution analyzed ; it contained a little iron, 

 not a trace of lime, but a considerable quantity of magnesia; hence 

 one might conclude that that part of the rock which is not chert, is 

 dolomite, while its included rhombohedra, which were set free on 

 solution, are magnesite; and a quantitative analysis is scarcely 

 necessary. 



The Geological Horizon. — The rock specimen was obtained from 

 the chert beds of the Niagara Limestone, which is homotaxial with 

 our Wenlock Limestone. It affords the oldest known instance of the 

 associated occurrence of siliceous sponge-remains and chert. On the 

 one side of a fragment of rock we find free spicules still siliceous, 

 together with quartz-crystals imbedded in dolomite — on the other a 

 mass of chert, in which spicules are rarely seen, and then usually as 

 hollow casts, but which contains remains once calcareous (such, as 

 the Polyzoon before mentioned) now converted into silex. 



Discussion. 



The President said this was the oldest sponge next to Proto- 

 spongia. The author's remarks ou it were most valuable, and those 

 on the collateral subject very interesting. It was to be hoped that 

 Mr. Maw would discover in the English Wenlock Limestone some 

 similar microscopic forms. 



Prof. Duncan said it was interesting to see the modern Hexacti- 

 nellids thus foreshadowed. Yery lately he had seen one of the 

 spicular forms described by Prof. Sollas in a form he had just 

 described. He quite agreed with the author in assigniug this form 

 to the Lyssakine Hexactinellids. There could be no question as to 

 the solution of the spicules in sea-water, as he had lately seen 

 evidence of it in specimens from deep-sea dredgings. The results of 

 Mr. Maw's washing promised to be very interesting. He had 

 examined many, but had not yet found either sponge-spicules or 

 Poraminifera. 



Prof. Rupeet Jones remarked that there are different kinds of 

 " chert,' 5 and expressed his opinion that Mr. Sollas had well 



