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195 
veins and cavities in the Mitcham rocks, very little of it has 
been observed under the microscope. 
Plate xxxiii., fig. 1, gives a general idea of the structure of 
this rock. 
M iit ia m, 
Macroscopic character s.—Very much finer in 
texture than i. This is probably due to its consisting of finer 
sediment originaliy, but the fineness of grain is also partly a 
secondary effect. Fracture and lustre as in i. Exactly simi- 
lar mineral composition. 
Microscopic charactenrs.-—Texture  mode- 
rately fine. Nearly all grains very angular, a few rounded or 
ovoid. Largest grains are round ones of felspar, quartz 
grains smaller and more angular. Mineral constituents in 
about the same proportions as in i. 
Quartz much shattered, almost every fragment showing un- 
dulose extinction. Inclusions not abundant, and without 
regular arrangement. Felspars of same types and general 
characters as in i, but showing very distinct evidence of 
strain in bending of twin lamelle and development of undu- 
lose extinction. A good deal of sericitic mica is developed 
around the periphery and occasionally in the mass of the 
felspars. 
A few moderately large flakes of muscovite are present, but 
most of the mica has a sericitic habit, and is evidently secon- 
dary in origin. In addition to the direct association of 
sericite with felspar a good deal is present as an interstitial 
cement. 
Finely granular dolomite also is abundant as a cement, and 
a few grains of pyrites, biotite, and tourmaline are included. 
Composite grains as in i. This rock differs from i. only in 
its finer texture, which is evidently chiefly the result of pres- 
sure, and in the presence of secondary sericitic and dolo- 
mitic cement. 
ur Dunstan Quarry, S10 yl 
Macroscopic characters —Exactly like ii. 
Microscopic character s.—Intermediate be- 
tween i. and ii. Texsure moderately fine, and evidently the 
result of cataclastic processes. АП grains show traces of 
rounding. Felspars less idiomorphic than in preceding types. 
Quartz much shattered, but still preserves traces of rejuven- 
escence of originally rounded grains. Sericite associated with 
felspar grains and distributed through slide as in ii. The 
amount of dolomite varies considerably in adjacent parts of 
the rock. In some sections it is entirely absent. 
Rutile needles, pyrites, and tourmaline grains are present, 
the last being bluish in colour. Some of the felspar grains 
contain small crystals of apatite. А 
