OCCURRENCE OF CALCITE IN A BASALT. 279 
These rocks had frequently been observed to contain 
little patches of calcite in the groundmass, but as a certain 
amount of alteration had generally taken place the presence 
of the calcite was put down to purely secondary causes. 
However, a specimen recently collected was found to be 
so rich in this mineral, while a good proportion of the rock 
was reasonably fresh, as to cause a suspicion that some- 
thing else than weathering was responsible for its presence. 
The specimen in question was found about three miles 
north of West Maitland, a short distance south of where 
the road to Helah crosses the North Coast Railway. On 
the property of Messrs. Comerford, between the homestead 
and the overbridge, is a small quarry, and in a creek, about 
thirty yards or so uphill from this, is the spot from which 
the rock was taken. 
The basalt is part of a thick flow, or series of flows, shown 
on Professor David’s map as extending for a considerable 
distance to the north-west of the spot described above, 
and at this place it underlies directly, with a dip to the 
east, some Coarse tough calcareous conglomerate belonging 
to the Harper’s Hill horizon, and very abundantly fossili- 
ferous, particularly in Aviculopecten. 
In this mass of lava amygdaloidal and massive varieties 
appear to alternate to a certain extent, indicating the 
possibility of a number of successive flows. 
The calcite-bearing type under present consideration is 
massive, and the rock directly above it is amygdaloidal. In 
the latter rock the plagioclase has been largely converted 
into analcite and natrolite (?), and the olivine is represented 
by pseudomerphs of green pleochroic iddingsite (?). A 
remarkable feature of the rock is the perfect freshness of 
the pale greyish-green augite. The spaces between the 
larger crystals and grains are filled partly with fine aggre- 
gates of felspar, ilmenite and indeterminate material, partly 
