MUSEUM OF COMrArwVTIVE ZOOLOGY. 



7 



McnomoncG region, but part of the Marquette district is included. The 

 .granites wcrechissed by him as igneous rocks. 



Printed in the midst of these reports is one from lAIcssrs. Foster and 

 Whitney (/. c, pp. G05-G2G) made to the Land Office and Interior De- 

 partment, dated November 5, ISiO, which gives some account of the Iron 

 and Copper districts. The iron is slated to occur in tiie mctamorphic 

 formation. "This formation consists of hornblende, talcose, and chlorite 

 slates, with associated beds of hornblende and felspar rocks, evidently 

 trappeau in their origin." (pp. GOD, GIO.) 



December ID, 184D, Professor J. D. Whitney gave some account of 

 this region before the Boston Society of Natural History.* Tlio iron 

 ore was then stated to be of igneous origin. In a ''report traus^ 

 mifctcd to the Interior Department, October 25, 1850,t Messrs. Fos- 

 ter and Whitney state that the sandstone is of Potsdam age. '^Eolow 

 the whole of the silurian rocks we meet with a class 'of deposites 

 which were probably detrital in their origin, but which have been 

 so metamorphosed as essentially to change their structure. They are 

 destitute of organic remains, and contain imperfect traces of strati- 

 fication. They consist of various schists and beds of quartz, marble, 

 and specular and magnetic oxide of iron. We have termed tlicsc vari- 

 ous groups the azoic system, ^n. system which, thus far, has not been 

 fully recognized in Europe, but the existence of which tlie results of this 

 survey, as well as that of Canada under Mr. Logan, have fully demon- 

 strated. Upon the upturned edges of those slates the Potsdam sand- 

 stone is found reposing in a nearly horizontal position. TJu^y form 

 the nucleus around which the newer rocks have boon deposited, and 

 arc extensively developed between the shores of the two lakes. They 

 are the depositories of the most extensive beds of iron known in the 

 world."i 'i'lio term '' Laurontian " was first proposed by Sir William 

 E. Logan, in 1853,§ for the mctamorphic rocks underlying the Pots- 

 dam sandstone north of the St. Lawrence, although it had^'been used 

 some years before by Mr. Edward Dcsor to designate certain drift de- 

 posits in the St. Lawrence valley, and by the law of priority the name 

 should have been retained in its original sense. 



May 5, 1851, a paper was presented to the American Association || 



* rrococdings, TIL 210-212. 



t Senate Docmuoiits, 2(1 Scss. 31st Cong., 1350-51, IT., Doc. 2, pp. 147-152. 

 X See also Bulk Soc. GcoL Franco, 1850-51, (2,) VIII. 89-100. 

 § llcport of Prof^n'eys Geol. Survey of Canada, 1852-53, p. 3. 

 Trocccdings, V. 4-7. 



