SOUTH MOSQUITO SECTION. 



133 



It is to be remarked that, as the scale of the map and sections was too 

 small to show all the intrusive sheets mentioned above, they have there 

 been generalized into two bodies, one of porphyry and one of porphyrite. 



south Mosquito section. On the south wall of Mosquito gulch, opposite the 

 cliff described above, a similar and equally instructive cliff section is found, 

 in which however there is no great fault ; only the slight dislocations marked 

 by shallow ravines, common to all the cliff sections. The beds on this cliff 

 were examined in some detail and careful measurements were taken, as it 

 was considered to be a type section. The series from the top of the cliff 

 downwards is: 



Feet. 



r Coarse granular gray limestone i with black chert 



I Blue lighter-colored limestone. 1 seams 60 



Lower Carboniferous . 1 Light-bluish limestone, weathering yellow 30 



I Blue limestone, generally thin-bedded 40 



130 



White Parting Quartzite, heavy-bedded, coarse at 



top 40 



Porphyrite,2 feet, thickeningto 20 feet farther west. 

 Silurian </ Limestones, light blue at top, gray semi-crystalline 



below; more silicious and shaly towards base 100 

 Very thin blue clay-shales, with shaly quartzite. . . 10 

 White quartzite, more or less calcareous 30 



180 



Shales, argillaceous and silicious, containing red- 

 cast beds 12 



Thin-bedded quartzite, with shale beds few inches 

 thick : 14 



White saccharoidal quartzite 18 



Porphyrite, G feet (thickens to the eastward). 



White saccharoidal quartzite, in beds from 4 inches 



to 4 feet 30 



Cambrian ^ Quartz porphyry, 30 feet. 



White saccharoidal quarrzite, massive above, thin- 

 bedded toward base; often discolored red and 

 brown on surface 35 



Quartz-porphyry, altered, 7 feet. 



Quartzite, iron-stained 1 



Quartz-porphyry, altered, 8 feet. 



White quartzite, conglomerate at base 40 



150 



. , i Gneiss, rich in mica 



' ( Granite, with red tabular feldspars 



