42 PEOF. T. G. BOXXEY OX THE HUEOlflAN SERIES 



Macroscopically it is compact in structnre, looking very like an 



argillite or felstone ; under the microscope it is found to be a rather 

 minutely crystalline granular dolomite, containing occasional gra- 

 nules of quartz, flakes of white and brownish mica (with probably 

 one or two grains of tourmaline), with haematite and opacite, and 

 occasional rather earthy-looking granules, chiefly occuiTing in streaky 

 bands and causing the peculiar weathering. All the minerals look 

 as if developed or completed in situ, so that the rock is a little more 

 altered than would be supposed from a macroscopical examination ; 

 still I feel doubtful whether to class it with these or with the former 

 group. 



There are some igneous rocks of interest associated with those 

 above described ; but as they have no bearing on the questions dis- 

 cussed in this paper, I pass them by without further notice. I may, 

 however, mention that when at Pagamaseng, a specimen was given 

 to me of a rock (diabase) containing in porphyritic crystals the 

 variety of anorthite called huronite. This was first described from 

 specimens of the same rock occurring as boulders near Lake Huron. 

 My specimen also came from a boulder near Pagamaseng, but 1 was 

 afterwards informed by Dr. Girdwood that the rock had been formed 

 in situ at no great distance from the settlement. 



The results described above may be thus briefly summarized : — 



(1) Putting aside rocks indubitably of igneous origin, and certain 

 others the position of which is not clear, the Huronians of the 

 Sudbury region obviously form a series separated from the Laurentian 

 by a long interval of time. Though here and there among them rocks 

 may occur the structure of which, inconspicuous from the first, has 

 been yet more obscured by subsequent micromineralogical change, the 

 majority are obviously of fragmental origin, and we need not hesitate 

 to claim for them a place among the stratified rocks, so that these 

 will carry the other less definite cases with them. 



(2) Among the rocks in this region at present referred to the 

 Huronian, two groups may be distinguished. One, where the alter- 

 ations of the matrix are comparatively slight, merely such micro- 

 mineralogical changes as are common in the older Palaeozoic rocks, 

 such as the deposit of secondary quartz, the partial micatization of 

 felspars, the formation of viridite, &c. : another, where the changes 

 are more strongly marked, where the enlargement of fragments, the 

 generation of mica (especially of brown mica), has taken place on a 

 larger scale, so that the original clastic character of the rock, though 

 stili to be discerned, is less obvious, and in the case of the smaller 

 constituents it is often difficult to decide whether they are clastic or 

 endogenous. 



(3) This distinction must indicate either (a) that selective metamor- 

 phism has produced marked eff'ects, viz., that diversity of material 

 has led to different results being produced by one and the same 

 cause, or (h) that we are dealing with a series of great thickness, 

 the deposition of which occupied a very long time, so that the lower 

 beds are more altered than the higher, or (c) that under the name 

 Huronian two distinct series are included. I am well aware that in 



