ON THE ARCHiEAN ROCKS OK OIIKAT IMilTAlN. 



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MareeandLochShiclseriesof Dr. Hicks. Concerninf; tho ITppor Lauren- 

 tiaii or Norian scries lam not yot prepared to offer an opinion. I believe, 

 indeed, that much of it is igneous rock, and so jnay not avail for pur- 

 poses of comparison at so great a distance. The other members that I 

 liavo seen do not recall to my memory any of tho Scotch rocks. It is 

 needless to say that the gabbros of Skye arc igneous in origin, and much 

 more modern than the norites of tho Upper Laurentian. 



The Gairloch and Ben Fyn sotics has a very considerable resemblance 

 to a suite of specimens from the White Mountains shown to me by Dr. 

 Sterry Hunt, and forming the series called by him Montalban. These, so 

 far as I have seen, are not generally well represeated in Canada, but I 

 think it very probable that it will bo found necessary to remove from the 

 Huronian certain schists now provisionally placed at its base, and regard 

 these as representatives cither of the Montalban group (which litho- 

 logically is represented by the great zone of Alpine schists at the Val 

 Trcmola, St. (iothard) or of the immediately overlying zone of schists 

 (schistrii lustrees, llttndner achiefer in part, &c.), concerning whose age in 

 the Alps such diverse opinions have been entertained. To this group 

 tho newer schists of the Highlands are probably related, and some at 

 least f)f the schists of Anglesey and of the south of England — though it 

 is possible the metamorphic rocks of Cornwall may be older. 



Some beautiful reddish felstones shown to me by Dr. Sterry Hunt, 

 members of the Petrosilex group, are singularly like the felstones at the 

 base of tho Pebidian of Wales (Arvonian of Dr. Hicks). The great 

 mass of the Canadian Huronian, of which I have now seen many specimens, 

 and examined carefully along a section of not a few miles, corresponds 

 rather closely with the great series of slates, grits, agglomerates, and lavas 

 which immediately underlies the Cambrian — viz., tho Pebidian (with 

 the Arvonian of Dr. Hicks). The Huronian is not a highly altered series. 

 I feel certain that the microscope will generally disclose its original con- 

 stituents. I suspect, then, that in many parts of Canada there is an 

 enormous break between tho Laurentian and Huronian, though here and 

 there this may be partially bridged over. Further, if we are to put any 

 trust in lithological chai'acter as a test of relative ago, I hold it impossible 

 to consider the Huronian older than the Montalban, or to con-elate it 

 with the Pietra Vei'de group of the Alps. I have made no reference to 

 the Taconic group of America, because I have rot had the opportunity 

 of studying it either in the museum or in the field. 



On the concordance of the MoUasca inhahltiuf/ both aides of 

 the North Atlmdic and, the intenuediate Seas. By J. (T^VTN 

 Jeffreys, LL.D., F.R.S. 



[A coramuniciition ordered by the Goiioral Coinniittcc tu be i)nn{(idi)>,extenso among 



the Ileporl.'^.] 



DumxG a short but delightful and interesting visit to North America 

 which I made in the summer of 1871, on the invitation of the lamented 

 Professor Agassiz, for the purpose of examining the MoUusca procured 

 by the late Count Pourtales in tne Gulf of Mexico, I took tlie opportunity 

 of inspecting also many other collections of North American Mollusca, 



l» 



