\ 
THE GEOLOGY OF MITTAGONG. ole 
locality is covered with dolerite which may represent a 
sill exposed by denudation. 
2.—b. Hssexites.—This rock is a variety of dolerite con- 
taining some orthoclase, a varying amount of biotite, with 
ilmenite and analcime, as well as the ordinary constituents 
of dolerite, i.e. plagioclase and augite. The majority of 
the basic rocks of Jellore have somewhat similar compo- 
sition, though biotite is rare. It will be seen that the 
chemical composition agrees fairly closely with Brogger’s 
essexite from Gran. Chant’s farm, Jellore, is situated 
between two hills of essexite, though here the rock is 
mostly decomposed into a brownish soil. It is surrounded 
on the north and west by tilted quartzites which have a 
crater-like appearance, as they stand a little above the 
level of the soft essexite. This oval neck of essexite is 
probably the parent of the sills of similar rock which appear 
quite uniformly underneath the Permo-Carboniferous shales 
in the neighbourhood. The rock occurs almost undecom- 
posed in Jellore Creek just above Chant’s smaller selection 
at the foot of Mount Jellore. (See Section IV., No. 6.) 
2.—c. Basalts.—Basalt occurs as dykes, necks and cap- 
pings. The two former have already been described. The 
basalt cappings form a very noticeable feature round 
Mittagong. They are usually easily identified from the 
fact that they have almost all been cleared by the settlers. 
They weather into a rich red soil very suitable for agricul- 
_ ture, and hence all such areas have been occupied for many 
years. The basalt usually occurs as angular boulders about 
the size of a football. These have a brownish weathered 
surface, often pitted with small holes, but are very hard 
within. This structure is due to jointing which lends itself 
to disintegration and is probably present many feet below 
the surface. Another example of this jointing occurs in 
the deep quarry at Dundas. The long ridges of basalt are 
