GRENVILLE SERIES OF EASTERN NORTH AMERICA 631 



and these sections afford data for determining the relative proportion 

 of Kmestone present. 



In the Burleigh-Chandos section given above the Jack Lake lime- 

 stone is essentially a body of pure limestone, while the Loon Lake 

 limestone band may be estimated to be about half limestone. This 

 gives a thickness of about 8,350 feet of Hmestone in that section out 

 of a total of 17,824 feet, that is to say, 46.8 per cent, of pure 

 limestone. 



The estimated thicknesses above referred to are as follows : 



FEET 



Huronian-Marquette Iron Range, Michigan, U. S. A.' 12,590 



Huronian-Menominee Iron Range, Michigan, U. S. A.^ 4j6so to 6,400 



Huronian-Penokee Iron Range, Michigan, U. S. A.^ i3>95o 



Huronian-Mesabi Iron Range, Minnesota, U. S. A.^ 6,800 to 8,800 



Huronian & Keewatin-Vermilion Iron Range, Minnesota, U. S. 



A.s 13,350 to 15,550 



Couchiching series in Rainy Lake District, Ontario, Canada^. .23,760 to 28,754 



With these may be compared : 



Belt Formation in Montana, U. S. A.^ 12,000 



Pre-Cambrian of Lewis & Livingstone Ranges, Montana, U. S. 



A.* 9,900 to 10,700 



1 C. R. Van Hise, and W. S. Bayley, "The Marquette Iron-bearing District of 

 Michigan" (Monograph), U. S. Geol. Survey, 1897. 



2 W. S. Bayley, "The Menominee Iron-bearing District of Michigan" (Mono- 

 graph), U. S. Geol. Survey, 1904. 



3 R. S. Irving and C. R. Van Hise, "The Penokee Iron-bearing Series of Northern 

 Wisconsin and Michigan" (Monograph), U. S. Geol. Survey, 1892. This thickness 

 is arrived at by adding to the aggregate thickness of 1,950 ft., given for cherty lime- 

 stone, quartz slate, and iron-bearing member an additional thickness of 12,000 ft. 

 for the upper slate member, which thickness is that of the Hanbury slate, which in 

 the Menominee Range is its equivalent. 



4 C. K. Leith, "The Mesabi Iron-bearing District of Minnesota" (Monograph), 

 U. S. Geol. Swvey, 1903. 



s J. M. Clements, "The Vermilion Iron-bearing District of Minnesota" (Mono- 

 graph), U . S. Geol. Survey, 1903. 



6 A. C. Lawson, "Annual Report of Progress," Geol. Survey of Canada, 1885, 

 p. 108 c. c. 



7 "Pre-Cambrian Fossiliferous Formations," Bull. Geol. Soc. Am., Vol. X, pp. 

 201-15. 



8 Bailey Willis, "Stratigraphy and Structure of Lewis and Livingstone Ranges, 

 Montana," Bull. Geol. Soc. Am., Vol. XIII, pp. 316-24. 



