1845.] 587 



hundred feet thick, and sometimes also by amygdaloid, with which 

 it is occasionally, although rarely, interstratified. Large rounded 

 fragments of the trap rocks of the lake, especially the porphyries, 

 occur abundantly in its conglomerates, and sometimes form entire 

 beds near the parent rock. Hence we perceive that volcanic 

 energy was active, or at least had not ceased, during the period 

 of its deposition. 



In general, however, this sandstone is composed of fine grains 

 of quartz and felspar, together with rounded particles of primitive 

 and trap rocks ; and it is important to remark, that no fragment 

 of the Silurian fossiliferous limestones, known to occur to the 

 northward towards Hudson's Bay and extensively on Lake Huron, 

 was ever noticed in its conglomerates. 



Grains of mica are sometimes abundant, especially near its con- 

 tact with granite. It is sometimes calcareous, the carbonate of 

 lime occurring also in veins. It is often ferruginous, and there 

 are sometimes between its strata thin layers of a black sandstone, 

 which crumbles easily into a black, heavy, and highly magnetic 

 sand, very plentiful on the beaches, and which Mr. Tennant in- 

 forms me is the titaniferous oxide of ii'on. On the islands called 

 " the Twelve Apostles," on the south coast, there are beds of 

 ferruginous red marl. In colour this sandstone is often variegated 

 — being red, white, grey, yellow, and dark reddish-brown. The 

 only metallic minerals found in it are iron and copper ores.* 



No organic remains having as yet been found in this sandstone, 

 and its junction with the Lake Huron limestone in the river St. 

 Mary's below the rapids being hidden by drift, water, or an 

 almost impervious forest, so as hitherto to have escaped notice, it 

 is difficult to determine with any confidence its place or age. There 

 seems no reason to think that it can be more recent than the old 

 red sandstone ; and when it is considered that it appears in the 

 St. Mary's at low levels, forming nearly horizontal strata at the 

 bottom of Lake George, whilst the horizontal fossiliferous lime- 

 stone of Sugar Island and St. Joseph's rises into higher ridges, so 

 as to make it appear highly probable that the sandstone occupies 

 the inferior position ; and that, moreover, a sandstone is known 

 very generally to underlie transition limestone in Canada and the 

 United States : when all this is taken into account it is, perhaps, 

 not unlikely that the sandstone in question may belong to the 

 Silurian rather than the Devonian period. On the other hand, its 

 appearance in unworn slabs, that must be near their parent rock 

 in the neighbourhood of Michilimackinac, where great beds of 

 gypsum occur, would seem unfavourable to this conclusion ; as 

 may also, perhaps, the red marly beds of the Twelve Apostles, 



This sandstone, although not observed in the river St. Mary below 



* The principal locality of the copper is about seven miles westward of the 

 eastern extremity of Port Keewawonan, where there is a vein of malachite, with 

 brown and earthy-blue copper, five or six feet wide. This occurs in conglo- 

 merate ; but the same minerals are found in trap-rocks near the same places. 



