1866.] MACFARLANE — ON CUPRIFEROUS BEDS. 7 



filled with what appears to be the same chloritic mineral which 

 occurs as a constituent in the first two rocks above described. It 

 is very soft and may be cut into small, slightly coherent slices. 

 These fuse readily to a black glass, which is slightly magnetic. 

 In fine powder its colour is light greenish grey, and by ignition 

 it turns dark brown, losing 5 . 85 p. c. of its weight. Hydroch- 

 loric acid decomposes it readily. On analysis, and calculation as 

 above described, it gave. 



Silica 30.59 



Alumina 26.07 



Protoxide of iron 22.01 



Lime 1.92 



Magnesia 12.36 



Water 7.23 



100.18 

 It will be observed that these results correspond much more 

 closely with the composition of delessite than that calculated from 

 the constituents dissolved by nitric acid from the rock first des- 

 cribed. The specific gravity of the rock, including the amygdules, 

 is 2 . 78. The colour of the fine powder is dark reddish-grey. 

 On ignition it turns brown and loses 2.33. Nitric acid dissolves 

 25.67, and hydrochloric acid 34.12 of its weight. In the 

 residue from treatment with the latter acid, no heavy dark 

 coloured constituent could be detected. From the above particulars 

 the following mineralogical composition is deducible. 



Delessite in amygdules and grains... 38. 



Labradorite 62. 



100 

 An occasional crystal of feldspar is met with in the rock, which 

 seems to be identical with that occurring in the matrix, and is 

 only partially decomposed by hydrochloric acid. 



The various bands of rock which underlie the Pewabic lode 

 have been intersected by a cross-cut, more than five hundred feet 

 in length, from the seventy fathoms level of the Pewabic mine. 

 This working has passed through the following rocks, the local 

 names and thicknesses (horizontally) of which are as follows : 



Trap 137 feet. 



Old Pewabic lode 34 ". 



Trap 85 " 



