3 I I W. It. C SMITH — ARCHEAN ROCKS WEST OF LAKE SUPERIOR. 



obliterate all traces of the original bedding planes in these coarse elastics. 

 In so far, therefore, as the conclusions of Van Hise and Purnpelly are 

 applied to the Lower Archean rocks of Canada northwesl of Lake Superior, 

 the writer regrets that he finds himself al variance with these eminent 

 authors, being a follower of Geikie in the belief that conglomerates do 

 not necessarily mark any stratigraphic discordance in these old rocks. 

 These conglomerates have not yet received the attention which they 

 deserve, and we may hope that a more detailed an 1 extensive study of 

 them will elucidate some of the problems of Archean geology. 



THE STEEP ROCK SERIES. 



Discordant in Character. — The Laurentian and Ontarian rocks hitherto 

 considered do not embrace all the presumably Archean rocks found in 

 this country. Mr Smyth, late of the United States Geological Survey. 

 recognized and described* a discordant series, which is almost undoubt- 

 edly of post-Keewatin age, about the shores of Steep Rock lake. 



Its Stratigraphy. — This Steep Rock series consists of the following hori- 

 zons in ascending order: 



I. Basal quartz conglomerate, sometimes represented by a massive 

 quartzite, estimated to be 430 feet thick. 



II. Lower limestone, dark and light bluish-gray, with the bedding 

 marked by clierty seams, weathering in relief. The upper part of this 

 formation is a characteristic breccia of limestone and trap fragments in a 

 matrix of consolidated calcareous floor; thickness, 500 to 700 feet. 



III. About 600 feet of a very soft, fissile, dull green, pyritiferous, vol- 

 canic ash, containing beds of jasper and iron ore. 



IV. Interbedded, coarsely crystalline, greenish-gray traps (probably 

 diorite), with layers of dynamic green schists ; thickness, about 1,000 feet. 



V. Upper calcareous green schist, with thin seams of limestone. 600 

 feet thick. 



VI. Upper conglomerate, varying from hydromica schist, with many 

 grains of quartz, to a rather coarse conglomerate. The inclosed pebbles 

 consist entirely of quartz and granite; maximum thickness, 100 feet. 



VI L. About 1,400 feet of light greenish-gray, close-tectured, massive 

 greenstone and greenstone schist. 



VIII. Agglomerate, 300 fee< thick. 



IX. Dark gray clay slate, of unknown thickness. Higher horizons 

 probably occupy the country to the south of the lake. 



Such are briefly the descriptions of horizons by Smyth in his admirable 

 memoir. The work since done by the writer in connection with the 

 rocks of this series suggests no important modification of them. 



♦ "Structural Geology ol Ste< p R >c1j Lake, ' >ntario," Am. .lour. Sei., vol. xlii, p. 317. 



