on American Geology, 95 



Birdseye divisions. The only fossil as yet found in these sand- 

 stones is a single Linr/ula from near Sault St. Mary, which may 

 be either of Potsdam or Chazy age. The sandstones in question 

 form the upper member of a series of strata which on Lake Supe- 

 rior attain a thickness of several thousand feet, and passing down- 

 wards we find a succession of limestones, marls and argillaceous 

 sandstones, interstratified with greenstone and amygdaloid, and fol- 

 lowed by about 2000 feet of bluish slates and sandstones, with 

 cherty beds containing grains of anthracite, the whole underlaid by 

 conglomerates, and reposing unconformably upon rocks of the Hu- 

 ronian system. The presence of such slates is the more significant 

 from the occurrence already mentioned of fragments of green and 

 black slates in the coarse grained sandstones near the base of the 

 Potsdam, at Hemmingford mountain, showing the existence of ar- 

 gillaceous shales before the deposition of the quartzites of the Pots- 

 dam ; these are perhaps more recent than the lowest shales of the 

 Primordial zone, to which however, palseontologically they appear 

 to belong. 



This Quebec group is of considerable economic interest inas- 

 much as it is the great metalliferous formation of North America. 

 To it belongs the gold which is found along the Appalachian 

 chain from Canada to Georgia, together with lead, zinc, copper, 

 silver, cobalt, nickel, chrome and titanium. I have long since called 

 attention to the constant association of the latter metals, particu- 

 larly chrome and nickel, with the ophiolites and other magnesian 

 rocks of this series, while they are wanting in similar rocks 

 of Laurentian age. Am. Jour, of Science (2) xxvi. 237. 



The immense deposits of copper ores in Eastern Tennessee, and 

 the similar ones in Lower Canada, both of which are for the most 

 part in beds subordinate to the stratification, belong to this group. 

 The lead, copper, zinc, cobalt and nickel of Missouri, and the copper 

 of Lake Superior, also occur in rocks of the same age, which ap- 

 pears to have been pre-eminently the metalliferous period. 



The metals of the Quebec group seem to have been originally 

 brought to the surface in watery solution, from which we conceive 

 them to have been separated by the reducing agency of organic 

 matter in the form of sulphurets, or in the native state, and mingled 

 with the contemporaneous sediments, where they occur in beds, 

 in disseminated grains iormmg fahlbands^ or as at Acton, are the 

 cementing material of conglomerates. During the subsequent 

 metamorphism of the strata these metallic matters being taken 



