Dr. BiGSBY on the Geography and Geology of Lake Huron. 205 



line range, but by the immense deposits of sand and rolled masses of rock 

 which are found in heaps at every level, both upon the continent and islands : 

 and since these fragments are almost exclusively primitive, and can in some 

 instances be identified with the primitive rocks in situ upon the northern shore; 

 and since, moreover, the country to the south and west is secondary to a great 

 distance, the direction of this flood from the north seems to be well esta- 

 blished. 



The boulders of granite, gneiss, mica-slate (rare), greenstone porphyry, 

 syenite, and various amygdaloids, are principally of such varieties of these 

 rocks as I have not met with in situ, either in the neighbourhood of Lake 

 Huron, or in a journey of 600 miles which I made to the east and north-east 

 of the lake, through the forests of the river Ottawa, 



Of mica-slate I met with only two fragments, of a brown colour, among the 

 trap isles. A fragment of serpentine was found in Drummond, on Blockhouse 

 Hill. 



The greenstone porphyries have a light-coloured base, and contain crystals 

 of red or white felspar — seldom of both in the same block. I have seen boul- 

 ders of the porphyry with red felspar, on the Ottawa, 500 miles to the east 

 of Lake Huron. The syenites are the same as those of Europe. 



The amygdaloids are often coloured brown b}* iron, and then contain almond- 

 shaped masses of epidote only. The green varieties contain nodules of agate * 

 and red jasper, white amethyst, epidote radiating upon layers of quartz and 

 small garnets. 



It can scarcely be doubted that these rocks will be found in situ somewhere 

 on the northern shore of Lake Huron, between the Missassaga and Pelletau's 

 Channel. It is there and on the Isle of St. Joseph that their boulders most 

 abound. Together with the fragments of the above-mentioned rocks, are 

 found others of trap, greenstone-slate, greenstone-conglomerate, jasper-con- 

 glomerate, and quartz rock. These occur in every part of the lake, but most 

 abundantly near their parent rocks. The conglomerates closely resemble 

 those which have been found on the northern shore in situ. The base of the 

 conglomerates is either quartz or greenstone. Of the quartzose conglomerate 

 the nodules consist rarely of white translucent quartz, sometimes of green- 

 stone ; and more commonly of red, green, brown, black, or parti-coloured 

 jasper. In some instances pieces of quartz — rarely of greenstone — are mixed 

 with those of jasper. The greenstone conglomerates contain nodules, either 



* Agates, jaspers, &c, are found abundantly as pebbles, on Lake Superior and about the Mis- 

 sissipi. 



