654 J. J. H. TEALL ON THE CHEMICAL AND 
We have now to discuss the bulk-analysis of the rock. Two spe- 
cimens were analyzed—one a moderately coarse-grained variety from 
Cauldron Snout, composed mainly of monoclinic pyroxene, felspar, 
magnetic iron-ore, and quartz, with a very small quantity of colour- 
less pyroxene, but no trace of bronzite; the other a medium-grained 
rock from the crags near the Roman station of Bourgovicus, which 
contained both bronzite and the colourless pyroxene, in addition to 
the ordinary constituents. Both specimens were somewhat altered, 
the felspars having here and there lost their individual action on pola- 
rized light, and chloritic minerals having been slightly developed. 
The fine powder of the rock was dried at 110°*. The titanic 
acid in I. was determined with special care. 
For purposes of comparison I have placed two analyses of the 
Connecticut diabase, and one of a rock of similar character from 
Spitzbergen, side by side with my own analyses of the Whin Sill. 
Lis i: eT. LY. Wi 
niO, .. ol-22 50°71 51°78 52°68 49-78 
TiO 2 a2 1:92 oe ag 2°97 
Al,O,.. 14:06 14:78 14-20 14-14 14:05 
FeO,.. 432 8°52 3°59 =» 14:86 
KeOr S710 8°95 8°25 9°79 si 
MnO". 0-16 0-31 0-44 0-44 0-13 
CaO"... Sie 8:21 10°70 9°38 9-44 
MgO .. 4:42 5:90 7°63 6°38 5°65 
KOS AZo 1:39 0°39 0°87 } 1°70 
Na O".. 255 2°76 2-14 2:56 
HOT. eas 1G 0°63 (loss) 1°60 (loss) ate 
COP ee ea 0°25 hes e a 
POV U20 is 0-14 : 
FeS, 0-49 ye e 
Loss ae ate ane ee 1-42 
99°67  100°48 99°89 99°79 100-00 
SD: Gites (2490 2:944 3°03 2°97 
I. Whin Sill. Cauldron Snout, Durham. Moderately coarse- 
grained variety. 
II. Whin Sill. Crags near Roman station of Bourgovicus, North- 
umberland. 
III. West Rock. W. of New Haven, Connecticut. Hawes, 
‘American Journal of Science,’ 1875, p. 185. 
IV. Mount Holyoke, Massachusetts. Hawes. 
V. Diabase. Giinze Island, in the Eisfjord. ‘ Petrographisch- 
geologische Beobachtungen an der Westkiiste Spitzbergens,’ 
Min. Mitth. Heft iv. 1874, p. 264. 
If we assume that the magnesia in I. is wholly present in the 
monoclinic pyroxene (and microscopic examination shows that this 
assumption is very nearly correct, only a very small quantity of 
chlorite being present), we can then construct the following table, 
* Jn all the original analyses contained in this paper the powder was first 
dried at 110° C, 
