480 T. W. E. DAVID, W. F. SMEETH, AND J. A. SCHOFIELD. 
As to the nomenclature of this specimen, its mineralogical con- 
stitution practically entitles it to a place among the limburgites, 
though it is undoubtedly more stony in texture than is usual with 
these rocks. 
A partial analysis gave the following results :— 
SiO, = 38-447 
Al,O, = 19°88 
Fe,O, = 13°46 
Some oxide of manganese is included with the alumina. This 
shows that the rock is ultrabasic in composition. The high per- 
centage of alumina is accounted for by the analcime which is 
present in considerable quantity. 
Limburgite, (No. 10). 
This rock is not unlike No. 9 in general appearance, but its 
texture is finer. Sp. gr. 2°91. 
Under the microscope it is seen to be a highly glassy rock, the 
glass being very free from crystallites and of a rich brownish 
yellow colour. Contained in the base are porphyritic augites and 
olivines, and a second generation of smaller augites similar to 
No. 9. Numerous small granules of magnetite are also present. 
(Plate 15, fig. 4). 
It is possible that this rock is but a more glassy portion of the 
mass from which No. 9 has come, and that this glass holds 
potentially the granular augitic base which is seen developed 12 
the latter rock. 
A partial analysis, for comparison with No. 9, gave the follow: 
ing :— SiO, = 38-997 
Al,O, = 11-72 
Fe,O,; = 15:26 
The percentage of alumina in this is much less than in No 9, 
and probably represents more accurately the common magia bd 
in this rock no analcime, so prevalent in the other, is observed: 
