EAST OP MOSQUITO FAULT. 



213 



crop of White Porphyry, somewhat in 'the form of a dike, parallel to the fault, 

 but with ramifying branches extending in various directions. This body 

 is interesting as being one of the few cases where the White Porphyry 

 could be seen to have been directly erupted through the Archean, and is 

 very probably the source from which the lower sheets of this rock have 

 spread out between the lower Paleozoic beds below the horizon of the 

 Blue Limestone ; it seems hardly of sufficient size, however, to account for 

 the. immense thickness of the main sheet of White Porphyry above that 

 horizon, and whose source, as already shown, is supposed to exist in the 

 White Ridge near the head of Four- Mile Creek. 



' On the east wall of Dyer amphitheater, in the upper part of the White 

 Limestone near the Parting Quartzite, are the deposits of the Dyer mine, 

 from which the mountain has derived its name. This mine is one of the 

 earliest discoveries of the district, antedating by many years that of the 

 carbonate mines, but owing to its great altitude and difficulty of access it 

 has been but intermittently worked. A section measured along a steep 

 hillside, with a slope of 32, just south of the Dyer mine, gave the follow- 

 ing thicknesses: 



Lower Carboniferous 



Silurian 



Feet. 



( Blue Limestone : 



\ Dark blue, weathering black, with black chert 150 



f Parting Quartzite: 



Sandstone and silicious limestone . . 10 



White Limestone : 



Thin-bedded, bluish limestone 35 



Light-blue limestone, couchoidal fracture, passing. 



into pinkish, clayey material 15 



Gray, semi-crystalline limestone 40 



Sanely lime tone, with some sandstone 30 



White, silicious limestone 10 



150 



140 



Cambrian . 



Lower Quartzite : 



Red-cast beds 10 



Reddish brown qnartzites 50 



White, saccharoidal quartzite 100 



1(10 



White Porphyry, 200 feet. 

 Archean Granite 



