468 J. H. COLLINS ON THE SERPENTINE AND 
parts of dande. It will be seen that this last column does not 
differ very widely from the composition given for the whole rock 
under a. 
a. b. C. d. é. # 
Water lost at 100°C... 0-4 i f 05i eae 
Se aonition ©: ein CO oe ee 150 | = 
Sinan See ee 45-43 47-40 5920 4401 4346 43:58 
‘Aiea oe ear 1993 1930 1210 11:95 2850 20-22 
Ferrous oxide ............ 3°98 ; 9°81 2°84 1 wy 
Hearn ondeen ead eae p66 f 1140 4 95.90 858 f | =e 
Ee ee ae 1198° 11:80 1220 1051 1708 13-79 
Te 934 775 747 1615 | Seanad 
Alkalies and loss......... — 1:05 Tei bry 9°25 1:50 1°86 
100:20 100°00° 99-05 10000 99:18 99°60 
The composition of the hornblendic constituent of this rock (d) is 
very nearly that of many pargasites, except that the proportion of 
peroxide of iron exceeds that of the protoxide. It has, however, 
none of the optical properties of pargasite, as it exhibits no distinct 
form or cleavage, either macroscopic or microscopic. 
The felspathic constituent (¢) is remarkably rich in lime, and also 
contains a good proportion of soda. Under the microscope it in- 
variably shows the well-known clouded appearance indicative of 
incipient decomposition (kaolinization). To this very general inci- 
pient decomposition the low percentage of alkalies is probably due. 
The coloured bands regarded as characteristic of plagioclase are only 
visible in a very few places, and never very distinctly. Regarding 
the peroxide of iron present as replacing alumina, and the magnesia 
as taking the place of lime (except the minute proportion due to a 
slight admixture of the hornblendic constituent), the composition 
given in analysis (e¢) agrees pretty well with that required for 
anorthite according to the typical formula adopted by Dana, which 
requires— 
Sili@ahuosuveaama seen 43°1 
AMIMIN Gn Se 36°9 
AMG 24. ous tae eee 
100:0 
Eyen as it stands, the analysis is very near that of the anorthite 
from Neurode, analyzed by Streng and quoted by Dana under that 
mineral (no. 19) in his ‘System.’ It is the same “ felspar” that 
was described by Prof. Bonney and analyzed by Mr. Hudleston 
(Q.J.G.8. vol. xxxiii. pp. 895-927). It appears to be character- 
istic of several of the rocks of the Lizard peninsula. 
Description of the Rock specimens sent in illustration of the 
Paper.—An examination of the specimens exhibited in illustration 
of this paper will, I think, afford important information as to the 
