648 J. J. H. TEALL ON THE CHEMICAL AND 
found impossible to remove all traces of the felspar, owing to the 
intimate manner in which it was intergrown with the augite. 
Monoclinic pyroxene, Cauldron Snout, from a moderately coarse- 
grained rock (sp. gr. about 3°30) :— 
Comp. Mol. Rel 
SILO Ba et a 49°03 8182 
AO tae. 5°46 533 
eOpogtiy..t 15°57 2167 
Nin@ ae. wee "22 31 
Cad MR AY..4 15°34 2746 
Me Oanury 11°66 2922 
Na,0(K,0) . 1:24 200 
40 Om daspest 81 
99°33 
A portion of the alkalies and alumina in this analysis may cer- 
tainly be referred to felspar. The total iron is reckoned as FeO. 
The most striking feature is the large excess in the number of 
molecules of Fe+Mg over the number of molecules of Ca. This 
cannot possibly be explained on the assumption that a visible mix- 
ture of two pyroxenes was analyzed, for care was taken to select 
a rock in which the rhombic mineral could not be recognized. To 
determine if possible somewhat more accurately the composition of 
the prevailing pyroxene, an isolation of the mineral from the 
coarsest variety of Whin Sill was effected. The greatest care was 
exercised, and every grain used in the analysis was passed before 
the eye under the microscope. 
if. iT, tt. IV. 
oe 
SIG ae a 50°71 50°21 48-41 8079 54:2 
lg Cane age 3°50 3°24 4-05 395 2°6 
eNO ge oe 2°36 149 740 
CO! epee 15°30 17°40 15:08 2099 14:0 
MMO Fi ca «me 0-81 37 52. 
CaO) ns Leoe 13°92 15:98 2860 19-1 
MeOr Coo 13°63 14:05 12°14 3043 20-4 
Na,O(K,0) 1:48 
TH Ore eso 1:17 (loss) LP 
100-00 98°82 99°58 
I. Pyroxene from West Rock, Newhaven, Connecticut. American 
Journal of Science, 1875, p. 185. W. Hawes on the Trap 
rocks of the Connecticut Valley. 
II. Striated pyroxene isolated from a basaltic rock from Kolter, 
Faroe Islands. Dr. A. Osann, ‘“‘ Ueber einige basaltische 
Gesteine der Faroer,” Neues Jahrbuch, 1884, Band i. p. 48. 
III. Striated pyroxene from the coarsest variety of the Whin Sill, 
2m. south of Tyne Head. Sp. gr. 3°33 (approximately). 
ITV. Molecular relations of ITI. 
In our pyroxene R:Si=1:1. B:R=1:148. Ca:Mg:Fe= 
