260 University of California Publications in Geology t VoL - 13 



produced by glaciation. The character of the sediments points 

 strongly to their deposition by streams, since the beds of greywacke 

 interstratified with the conglomerate are not extensive sheets, but are 

 discontinuous and lenticular, having been observed often to end 

 abruptly against steep former embankments of pebbles. The exten- 

 sive beds of clay and sand covering much of the present surface, which 

 were left by the Pleistocene glacier, make a striking contrast with the 

 limited beds of greywacke which characterize the Cobalt Series. 



The Diabase Sill 



On northwest sections constructed through the two Keewatin roof 

 blocks of the diabase sill, on the King Edward and Nova Scotia prop- 

 erties, respectively, the sill is found to have an average thickness of 

 1000 feet. The same approximate thickness was found at the Timis- 

 kaming property, where the shaft was sunk through the sill. At Kerr 

 Lake the base of the sill plunges down across the tilted Cobalt Series, 

 making an angle of 40 degrees with the beds, which slope at 10 de- 

 grees in the same direction ; also on the west side of Peterson Lake the 

 sill cuts across the sediments at a low angle, and down into the 

 Keewatin ; while at the Shamrock Mine the upper contact of the sill 

 and the Keewatin takes a vertical attitude. The Keewatin roof blocks 

 lie between conglomerate areas on the under side of the sill, and 

 hence must have been elevated vertically a distance of approximately 

 1000 feet. Evidently the sill was not injected in an even horizontal 

 position, but only roughly approximated it, plunging at one point 

 and arching at another, the contacts and the whole configuration of 

 the mass being uneven. Attention must be called especially to the 

 great, plunge taken by the sill between Kerr Lake and the west shore 

 of Peterson Lake, which area was probably originally covered by a 

 continuous sheet of conglomerate. The Keewatin roof blocks lie 

 approximately along the axis of the depression. This is explained by 

 the injection of the sill downward beneath the Cobalt Series into the 

 Keewatin basement, and the lifting of the roof. The erosion of this 

 lifted mass resulted in the almost complete removal of the conglomer- 

 ate sheet, and the leaving of only three small remnants of Keewatin 

 resting upon the sill ( see fig. 2 ) . 



It has been noted in the Rochester and neighboring properties that 

 offshoots from the sill penetrate the Keewatin of the roof for short 

 distances, and that blocks of Keewatin are found imbedded in the sill, 

 representing fragments of the roof or floor torn loose by the moving 

 magma during its injection; while in the Beaver Mine a block of 



