152 
hard, of a reddish brown colour, has a moderately straight 
fracture, and a pinkish white streak, and its specific gravity 
is 2*92. 
Three average samples of the rock were taken, two from 
the north and one from the south side of the beck. All of 
them were more or less decomposed by exposure to air 
and moisture, but No. 26 much less than Nos. 23 and 24. 
Professor Roscoe on analysis, found their present chemical 
composition to be as follows : — 
South of 
Stream, 
No. 23. 
North of 
Stream, 
No. 24. 
North of 
Stream, 
No. 26. 
Silica 
45-54 
24-76 
7-70 
13-84 
057 
2-78 
4-82 
50-96 
24-20 
14-48 
7-32 
0- 55 
1- 90 
0-59 
51-10 
21-58 
9-40 
6- 24 
1- 33 
2- 70 
7- 65 
Peroxide of Iron 
Alumnia 
Lime 
Magnesia 
Carbonic Acid 
Alkalies, Water (by difference) ... 
100-00 
100-00 
100-00 
The only rock which I know of a similar composition, is 
a probable variety of green earth, resembling a decomposed 
pyroxene, described by Macfarlane, in the Canadian 
Naturalist, New Series, vol. iii., No. 1, page 5, in a paper 
on the cupriferous bed of Portage, Lake Michigan, which 
consists of — 
Silica 46*48 
Alumnia 17*71 
Protoxide of Iron 21*17 
Lime 9*89 
Magnesia trace 
Alkalies (by difference) 1*97 
Water 2*78 
Mr. David Forbes, F.R.S., to whom were forwarded small 
specimens of the rocks and the above analyses, kindly 
informed me that the rocks were so much decomposed that 
it was difficult to pronounce with certainty as to what they 
