424 PROF. T. G. BONNEY ON THE MICROSCOPIC STRUCTURE 
mineral resembling an alteration-product after biotite, grains of 
iron-oxide, and a fair amount of quartz. The felspar agrees best 
with oligoclase or albite. The rock has evidently been much 
crushed and recemented, and much of the quartz has the aspect of a 
secondary constituent. It is a quartz-diorite. 
23 (Dyke, near Fort Doyle)—In all probability this rock has 
once been a basalt, but the felspar has been replaced by secondary 
microliths of more than one kind, until the original structure is 
practically obliterated; and the other constituent is a green, rather 
filmy, irregularly crystallized mineral, which is, in part at least, 
hornblende. There are some scattered granules of iron-oxide.’ 
37 (Between Forts Doyle and Le Marchant), and 39 (Howmets, near 
Cobo, 2 male east of Cobo Bay).—It is a little difficult to say whether 
this rock should be called a quartz-syenite or a quartz-diorite, for 
the felspar is so much altered and replaced by secondary microliths. 
From the small portions which remain unaltered I should infer that 
plagioclase predominated, and class the rock with the latter. There 
is a considerable quantity of hornblende and biotite, both rather 
altered. The quartz, of which there is a moderate amount, contains 
numerous cavities, in which are generally small moving bubbles. 
43 (Portinfer).—Has a general resemblance to the above, but is 
perhaps rather more distinct; a quartz-diorite. 
30 (Fermain Bay).—Also a quartz-diorite with mica ; some apatite 
is present, and probably a little sphene. 
14 (Castle Cornet, at boundary of Gneiss)—A rather coarsely 
crystalline rock, consisting mainly of green hornblende, a very de- 
composed felspar, probably plagioclastic, with some altered bictite. 
There is also a fair quantity of apatite and sphene, with, of course, 
some iron-peroxide. The rock is a diorite. 
7 (Near Fort Le Marchant)—The hornblende and felspar are yet 
more highly altered, but the rock is probably a true diorite ; there 
is a fair amount of a white mica, probably hydrous. 
41 (Bon Repos Bay).—Consists mainly of well-crystallized horn- 
blende, some brown mica, iron-peroxide, a plagioclastic felspar (not 
abundant), probably oligoclase, and a little apatite. The slide is not 
a very good one for examination; but field-evidence, I am told, 
proves it to be a true diorite. 
6 (South of Fort Doyle).—Consists mainly of hornblende, with 
probably a little altered biotite and some decomposed felspar. Some, 
at least, of the hornblende has the look of a secondary product. At 
present the rock may be regarded as an abnormal diorite or a horn- 
blendic diabase; but I should think that very probably it was once 
a gabbro, rich in the pyroxenic constituent. 
35 (Fort Doyle).—A diorite, with a little free quartz and apatite, 
somewhat crushed and decomposed. 
36 (Fort Doyle).—The constituent minerals are quartz, felspar, very 
much decomposed, and a filmy, green, chloritic or micaceous mineral. 
I cannot give the rock a name, for it appears to me that the slide 
has been cut from a specimen which has been exposed to great local 
crushing, and subsequently recemented. (See 35 and 45 E. H.) 
t 
