AT (a.EASTON, IN LOW FURNESS. 



93 



Silica 



Peroxide of iron 



Alumina 



Lime 



Magnesia 



Carbonic acid 



Alkalies, Water (by difference) 



South of 

 stream, 

 No. 23. 



45'54 



24*76 



770 



13-84 



o'57 

 2-78 



4-82 



North of 

 stream, 

 No. 24. 



5096 

 2420 

 14-48 



7"32 

 0-55 

 190 



0*59 



North of 

 stream, 

 No. 26. 



5110 

 21-58 

 9-40 

 6-24 

 133 

 270 

 7-65 



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 Na- 

 turalist/ 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 



Alumina i7'7i 



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 decom- 

 posed that it was difficult to pronounce with certainty as 

 to what they were, but he was inclined to think that they 

 were an intrusive dolerite of carboniferous age rather than 

 a melaphyr. The iron had been changed from a protoxide 

 into a peroxide, and the lime had resulted from the de- 

 composition of a lime felspar. As Mr. Forbes had found 

 the presence of titanium united with iron in all the carboni- 

 ferous dolerites he had examined, I took several ounces 

 of the three samples above given, and having heated them 

 in a crucible, so as to convert the iron from a per- into 

 a protoxide, extracted it by a magnet. About half an 

 ounce of this iron was very carefully examined bv Mr. 



