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 liodies, one of porphyry and one of porphyrite. 



South Mosquito section. — On the soutli Wall of Mosquito gulcli, opposite the 

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

 in which however there is no great faiilt ; 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. 



{Coarse grauular gray limestoue i with black chert 



Blue lighter-colored limestone. ) seams 60 



Light-bluish limestone, weathering yellow 30 



Blue limestone, generally thin-bedded 40 



\ White Parting Quartzite, heavy-bedded, coarse at 



top \ 40 



Porphyrite, 2 feet, thickening to 20 feet farther west. 

 Silurian } Limestones, light blue at top, gray semi-crystalline 



below; more silicious and shaly towards base . . . 100 

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

 White quartzite, more or less calcareous 30 



r 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 quartzite, massive above, thin- 

 bedded toward base; often discolored red and 

 brown on surface 35 



Quartz por[)hyry, altered, 7 feet. 



Quartzite, iron-stained 1 



Quartz pori)hyry, altered, 8 i'eet. 



White quartzite, conglomerate at base 40 



130 



180 



150 



, , ( Gneiss, rich in mica. 



Archean } ^ . ' 



( Granite, with i-ed ta 



bular feldspars 



