68 PEOCEEDIHGS OP THE GEOLOGICAL SOCIETY. [XoV. 23, 



The calcareous septa in this specimen are very thin, and are trans- 

 verse to the plane of contact of the two minerals ; yet they are seen 

 to traverse both the pyroxene and the serpentine without any inter- 

 ruption or change. Some sections exhibit these two minerals filling 

 ^ adjacent cells, or even portions of the same cell, a clear line of divi- 

 sion being visible between them. In the specimens from Grenville, 

 on the other hand, it would seem as if the development of the Eozoon 

 (considerable masses of which were replaced by pyroxene) had been 

 interrupted, and that a second growth of the animal, which was re- 

 placed by serpentine, had taken place upon the older masses, filling 

 up their interstices. 



The results of the chemical examination of these fossils from dif- 

 ferent localities may now be given : — I. A specimen of Eozoon from 

 the Calumet, remarkable for the regularity of its laminated arrange- 

 ment, gave to warm acetic acid 27'0 per cent, of soluble matter, con- 

 sisting of carbonate of lime 97"1, carbonate of magnesia 2-9 = 100. 

 II. Another specimen of the fossi], from Grenville, replaced by 

 pyroxene, yielded in the same way 12'0 per cent, of soluble matter, 

 which was composed of carbonate of lime 98-7, carbonate of mag- 

 nesia 1-3=100. III. In this specimen of the fossil, which adjoined 

 the last, serpentine was the replacing mineral. The soluble portion 

 from this equalled 47*0 per cent., and consisted of carbonate of lime 

 96-0, carbonate of magnesia 4-0 = 100. It thus appears that the 

 septa in these specimens of Eozoon are nearly pure carbonate of 

 lime. The somewhat larger proportion of magnesia from the last 

 is due to the use, as a solvent, of dilute nitric acid, which slightly 

 attacked the serpentine. 



The pyroxene of the above specimens is a very pure silicate of 

 lime and magnesia ; that from I. gave, by analysis, silica 54-90, lime 

 27-67, magnesia 16-76, volatile matter 0-80 = 100-13. A partial 

 analysis of the pyroxene from II. yielded lime 28-3, magnesia 13-8. 

 This specimen was interpenetrated with serpentine, amounting to 

 about 10-0 per cent., which was first removed by the successive 

 action of heated sulphuric acid and dilute soda-ley. The serpentine 

 from III. yielded silica 42-85, magnesia 41-68, protoxide of iron 

 0-67, water 13-89=99-09. As already mentioned, this serpentine 

 had lost a little magnesia from the action of nitric acid ; a similar 

 serpentine from the Calumet, associated with the Eozoon, gave silica 

 41-20, magnesia 43-52, protoxide of iron 0-80, water 15-40 = 100-92. 

 These serpentines from the Laurentian limestones are remai'kable for 

 their freedom from iron-oxide, for their large amount of water, and 

 their low specific gravity *. 



Specimens of Eozoon from Burgess differ from the foregoing in 

 the composition both of the replacing material and the septa. The 

 latter consist of a somewhat ferriferous dolomite, the analysis of 

 which was made upon portions mechanically separated from the 

 enclosed silicate ; it yielded carbonate of magnesia 40-7, carbonate 

 of lime, with a little peroxide of iron, 59-0 = 99-7. The septa of the 



* See my descriptions, ' American Journal of Science,' 2nd ser. vol. xsvi. p. 236, 



