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= NOTES ON ANTARCTIC ROCKS. 483 
would indicate a felspar, is to be found among the colourless 
granules; nevertheless some of them were found to be biaxial in 
convergent polarized light. Further, in the neighbourhood of 
joint planes, some of these granules are seen to be slightly decom- 
posed, indicating that they are silicates and not quartz. 
These silicates, from their resemblance to the quartz grains, 
when not decomposed, may be either felspars or scapolites or both. 
The fact that many of them are biaxial may reasonably be taken 
as indicating felspar, notwithstanding the absence of twinning, for 
the secondary felspars in schists are frequently untwinned and 
much resemble quartz in thin sections, The question then arises 
as to whether a member of the scapolite group is also present. 
To try and settle this, a prolonged separation of the mineral con- 
stituents was made. A few heavy minerals came down first, 
then the tourmaline; close on this came the dark mica, and 
immediately after it the muscovite. The bulk of the rock, which 
now .consisted of colourless grains only, remained. For a long 
time we tried to separate this into its different constituents but 
failed, as they all floated or sank together. It followed therefore 
that the quartz, felspar and other silicates, not only resembled 
each other under the microscope but were also of equal density. 
_ Separation by this method having failed, and the silicates being 
but slightly attacked by acids, the isolation and identification of a 
Scapolite (if present) is not feasible. Nevertheless certain general 
arguments render the presence of such a mineral very probable. 
In the first place a felspar with the sp. gr. of quartz would have 
& composition approaching that of oligoclase or andesine. In 
_ a felspar the proportion of CaO does not exceed that of 
Na,0, and if we assumed that all the Na,O was present in 
felspar, this would account for only 2:1% of CaO, leaving a balance 
of PTZ, unaccounted for. We are therefore in need of a silicate 
Which, under the microscope resembles quartz, has the same sp. gT- 
“8 quartz, and in which the amount of CaO, or the proportion of 
CaO to Na,0, is large. 
