190 PKOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 10, 



The Connemara Ophite contained what we had no doubt had been 

 taken for " chamber-casts ; " but these parts differed in one respect 

 considerably from those belonging to the Grenville variety. We had 

 got the impression that in the latter they were rarely arranged other- 

 wise than in laminae ; but in our home rock we found them to have a 

 decidedly " acervuline " arrangement, and to be seemingly distin- 

 guished by some other characters. 



In this dilemma we made free to apply to Sir "William Logan, 

 •^vho very kindly supplied us with specimens from Grenville. These 

 assisted us materially ; for we now saw that the " acervuline '* 

 arrangement of the '' chamber-casts " was likewise a characteristic 

 feature of the Canadian Ophite. Still the two rocks presented some 

 important differences. As we informed Sir William Logan, the 

 " chamber-casts " in the variety from our locality varied considerably 

 in size, some being large, often as much as half an inch in diameter, 

 and others extremely small; while the septa are often very thin, 

 resembling in this respect the cell-walls of ordinary vegetable tissue 

 (parenchyma), and frequently the contrary, in many instances mea- 

 suring half an inch in thickness. The contrast between the 

 " chamber-casts " and the septa was not strikingly obvious, owing to 

 the paleness of the green colour of the former and the greyish 

 whiteness of the latter. Besides, the septa showed no decided 

 appearance of being traversed by structures representing the " canal 

 system." We also felt unconvinced of having detected undoubted 

 examples of the '' proper wall " or asbestiform layer. 



At last, by mere accident, we procured from a dealer in Galway a 

 specimen, cut in imitation of a bottle, containing " acervuline " 

 patches, in which the " chamber-casts," composed of what we con- 

 sider to be loganite*, and the septa, consisting of white calcite, 

 were as decidedly in contrast as in Canadian specimens : the agree- 

 ment was still closer, as the "walls" were of ordinary thickness, and 

 they appeared to contain representatives of the " canal system." 

 This proved to be the only specimen we could procure in Galway ; 

 but learning from the dealer that he recollected where it was got, 

 we determined on taking him as our guide to the place and trying 

 to procure more of the same variety. 



We had the good fortune to be accompanied in our excursion by 

 Professor Harkness, who, however, soon showed himself to have no 

 sympathy with us in the view we then held, being as much a dis- 

 believer in " Eozoon Canadense " as Mr. Bailey, who, a few days pre- 

 viously, had publicly declared his doubts that the " thing in question 

 was a fossil at alP'f. Our "compagnon de voyage" argued for its 



* We learn from a paper by Professor Haugbton, inserted in the ' Journal of 

 the Geological Society of Dublin,' vol. v. p. 128, that the Rev. Joseph Galbraith 

 analyzed a specimen of Connemara Ophite, and proved it to be a hydro-mag- 

 nesian silicate, with a little lime and iron peroxide, from which we infer that it 

 is impure. Doubtless the rock varies much according to locality: we have 

 found specimens containing so much alumina as to show their close relationship 

 to loganite. 



t Meeting of the Royal Geological Society of Dublin, held April 12th. Mr. 

 Bailey has since published his view in a note added to his paper on " The 

 Cambrian Rocks of the British Islands." See ' Geological Magazine,' vol. ii. p. 388. 



