IN THE NEIGHBOURHOOD OF SUDBURY, CANADA. 39 



the rock ; its structure resembles that of some devitrified felstones ; 

 also, though more coarse, that of the TrefFgarn hiilleflinta. 



Bearing some resemblance to this, but more distinctly fragmental 

 (it contains a yellowish fragment, about 1 J" x 5", together with some 

 little bits), is a small specimen sent by Dr. Selwyn, labelled " 1 mile 

 W. of Sudbury." The matrix consists of granules of crystalline 

 quartz and the usual brown or greenish-brown mica, with occasionally 

 a larger grain of quartz or of felspar. I have little doubt that all 

 the constituents, if not developed in situ, have been enlarged, but I 

 cannot detect the original boundary of any one. The fragments 

 contain but little mica, and chiefly consist of granules of quartz much 

 smaller than in the matrix, with rather more ferrite scattered among 

 them. The slide includes a portion of the larger fragment and some 

 of the smaller ; all can be distinguished, but they are, as it were, 

 ^' fused " into the matrix. 



The next set of fragments are of a grey-speckled crystalline rock, 

 which often occurs of large size and in great abundance. The 

 matrix exhibits a structure identical with that just described, but 

 the grouped quartz grains therein are rather larger in size, while the 

 felspar-crystals are all larger and more distinct. These certainly 

 give one the idea of being encroached upon by the matrix, as their 

 actual outlines are so very irregular, and occasionally there appears 

 a kind of intrusion of the matrix, but there is not, as one would 

 expect, any appreciable amount of white mica formed. There are, 

 however, in the slide, some yellowish mineral granules, and an occa- 

 .sional larger yellow-grey grain, which may be an alumina silicate. 

 On the whole, then, I think it highly probable that these have once 

 been a porphyritic rhyolite, though they have been subsequently 

 greatly altered by molecular rearrangement. 



The fragments with the dark hornblende-like crystals have a 

 similar matrix, but it seems to contain more felspar ; at any rate 

 the " dusty " look of a considerable proportion of the granules indi- 

 cates clearly the position of what is, or has been, this mineral. 

 There is also more ferrite, opacite, or an impure chlorite (?) scat- 

 tered about the slide than in the other cases. We find the compound 

 grains of quartz and the porphyritic felspar in the condition already 

 described. The supposed hornblende proves generally not to be a 

 perfect crystal, but an irregularly outlined group of associated flaky 

 grains of hornblende or chlorite (some a very dark indigo-green, 

 others practically opaque) "clotted" together, with occasional in- 

 terspersed quartz-grains. Where these flakes are cut transversely 

 they show cleavage, are dichroic, and extinguish either parallel or at 

 small angles with the cleavage. There is, however, in one slide a 

 fairly perfect crystal, which is undoubtedly hornblende, and on the 

 whole I am disposed to refer most of the granules to this mineral 

 rather than to one of the chlorite group. The pale-brown mineral, 

 looking like granules of gum, mentioned above, is not uncommon 

 here. It would therefore appear probable that this rock also may 

 be of igneous origin, but changed like the other. 



The last to be described are the breccias (less coarse) at the greatest 



