302 GEOLOGY AND MINERALOGY. 



shields of Infusoria, and may piny an important part in the consolidation of the 

 ocean sediments and the sililication of organic remains."* 



AZOIC ROCKS OF CANADA. 



Professor Whitney in an article in the May number of Silliman's Journal, takes 

 exception to Sir William Logan's subdivisions of our Azoic rocks. He contends 

 that the so-called Huronian Formation belongs in part to the Polsdam sandstone, 

 and in part to the underlying Laurentian group; and, further, that the latter 

 should simply be called " Azoic," to the exclusion of the term " Laurentian" — 

 this term having been already bestowed by Desor on the local, post-tertiary beds 

 of Beauport, and otlier places, in the valley of the St. Lawrence and elsewhere. 

 Without attempting, in the present place, to discuss the claims of the Huronian 

 rocks to be considered a distinct formation, we may reasonably call in question 

 the justness of that view, which, by collecting all of our unfossiliferous strata 

 into a single group, would represent them as the products of a single epoch 

 or period. Surely, if the Palaeozoic age be looked upon as typical of at least 

 four periods in the history of the Earlh, a subdivision of some kind may be equally 

 conceded to the formations of the great Azoic age: although from the absence 

 of fossils, the subdivision of these formations may be a work of more difficult 

 attainment. That such will some day be effected however, and to a greater extent 

 than many geologists may at present be willing to allow, we are fully confident. 

 With regard to the term Laurentian as applied to some of these Canadian rocks, 

 we would observe, that, even if the same term were previously applied to the 

 patches of post-tertiary strata alluded to above, its peculiar fitness for the 

 gneissoid rocks of the Laurentian Kange and connected country, would fully 

 warrant its retention. On the other hand, we quite ngree with Professor Whituey 

 respecting the use of the term " Cambrian." If this term cannot be applied in 

 accordance with the views of Sedgwick to the whole of the lower Silurians (a 

 conclusion becoming more and more apparent every day,) let it be abandoned 

 altogether. Its application to the Huronian formation, or to the Potsdam sand- 

 stone as proposed by Sir Charles Lyell, answers no object whatever, and is but 

 little likely, moreover, to be generally adopted. 



SUPPOSED EMERALDS FROM ALGIERS. 



The pale green crystals from the Upper Valley of the Harrach in Algiers, an- 

 nounced as emeralds by M. Ville, have proved to be tourmalines, analogous to the 

 somewhat rare variety met with at St. Gothard, and in Elba. They were first 

 discovered in 1855, in a crystalline limestone associated with gypsum and diorite, 

 about ten miles east of Blidah. (Bulletin de la Societe Geologique de France; 

 tome XIII, page 416.) Most tourmalines when treated with salt-of-phosphorus 

 before the blow-pipe, effervesce and dissolve readily, but this pale green variety, 

 curiously enough, behaves just like the emerald : exhibiting a scarcely perceptible 

 effervescence, and dissolving very slowly. 



CYSTIDEANS. 



Mr. Billings, palaeontologist to the Geological Survey of Canada, has discovered 

 in the Chazy limestone near Montreal, a new Cystidean, more or less allied to 

 Cryptocrinus by its three basal or pelvic plates, but differing from that genus by 



* Some, although probably but a small portion, may be taken up by marine vegetation, 

 as seven percent, of silica appears to have been detected in the ashes of fuc-us vesiculosus. 

 The ashes of most sea-weeds, however, contain no more than one or one-and-a-half per 

 cent, of silica. E J. C. 



