210 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 24, 



The loss arises from the carbonic acid which is not here represented 

 as combined with the excess of lime and magnesia. 



The compact ivory-like fragment from Riviere Quelle had a sp. 

 gr. of 3'035 to 3" 150. It gave out ammonia and water with an ani- 

 mal odour when heated, and with sulphuric acid the vapours corroded 

 glass, indicating a fluorid. It contained a larger proportion of car- 

 bonate of lime and magnesia, and more oxide of iron, than the hollow 

 bone from the same locality. 100 parts of it gave — 



Phosphate of lime 40*34 



Carbonate of lime and some fluorid 5*14 



Carbonate of magnesia 9*70 



Oxide of iron, with a little alumina and manganese 12*62 



Insoluble siliceous matter 25*44 



Volatile 2*13 



95*37 



The analysis is defective from a loss of over 4 per cent., but the 

 quantities actually found show sufficiently well the composition of 

 the substance where scientific accuracy is not essential. 



Before returning to the foot-prints, I would further state, on the 

 subject of phosphatic nodules, that last season my associate, Mr. 

 Murray, in examining the rocks on which the Lower Silurian un- 

 conformably rests in the Johnstown District, met with altered con- 

 glomerates interstratified with limestone not distinguishable from the 

 highly crystalline rock which is interstratified with the gneiss ; and 

 associated with the quartz-pebbles of the conglomerate are soft white 

 nodules containing phosphate of lime. In the beds of the crystalline 

 limestone, separating the masses of gneiss, imperfect crystallizations 

 of phosphate of lime are of very frequent occurrence. They are 

 usually small, but in some parts they become large and so thickly 

 disseminated as to give the rock an economic value. On Lake 

 Huron the Lower Silurian group rests unconformably upon a sili- 

 ceous series with only one known band of limestone, of about 150 

 feet thick, with leaves of chert in abundance, but as yet without dis- 

 covered fossils. This series is supposed to be of the Cambrian epoch. 

 It comprehends the copper-bearing rocks of that district, and with 

 its igneous interstratified masses has a thickness of at least 10,000 

 feet. The gneissoid group, of which mention is made, is probably 

 still older than this. Its conditions appear to me to make it reason- 

 able to suppose that it consists of aqueous deposits in an altered 

 state, and the origin of the phosphatic nodules and crystals in some 

 of its members, with reference to a possible connexion with life in 

 such ancient strata, becomes a question of great interest. 



Having shown, I hope conclusively, the stratigraphical relations of 

 the track-beds, I have only farther to state that, with the view of 

 submitting to competent authority as large an amount of evidence as 



