Page:A sketch of the physical structure of Australia.djvu/58

46 but from the latitude of Adelaide about north till it terminates near lat. 29° and 30° in the singular horse-shoe shaped depression of Lake Torrens. Its length is thus about 400 geographical miles. None of its peaks ever much exceed 2000 feet in height, but it is broken into many ranges, often having the peaked and serrated character of a mountain chain in miniature. About Cape Jervis I was informed the rocks were chiefly mica slate and gneiss; in the hills behind Adelaide, I found much chloritic slate and similar rocks, but north of that for about 50 miles, or as far as the mines of Kapunda, the rocks of this chain seemed to be principally clay slate.

Wherever I saw the dip of the rocks shewn, it was to the S.E. at pretty high angles. This would put the clay slate under the gneiss, mica, and chlorite slate, but my observations were so few that the inference is not to be depended on. The only observation on the cleavage I made was about five miles N. of Gawler Town, where both the cleavage and the bedding of the clay slate dipped S.E., the cleavage at a higher angle than the bedding. Many large white quartz veins traversed the clay slates, all the peaked eminences being apparently composed of white quartz. Around Kapunda, though in the heart of the chain, the country was only gently undulating. The mines are about a quarter of a mile N. of the bed of the River Light. Though nothing but hard clay slate was to be seen in the adjacent country, the rocks near the mines are all soft,—generally a blue, white, or pinkish