BASALTS OF BATHURST AND NEIGHBOURING DISTRICTS. 303 
are probably calcite. Under the microscope the rock is uniformly 
micro-porphyritic. The porphyritic constituents are augite and 
olivine, with a few moderate sized felspars. Most of the felspar, 
however, exists as very small lath shaped crystals scattered 
through the ground mass, They are gathered round the larger 
crystals and shew flow structure beautifully. Mr. Curran has so 
well described the crystals in detail that it is unnecessary to 
repeat. He considers the magnetite, which is abundant, to be a 
primary constituent of the basalt, it having been one of the first 
minerals to crystallise out from the magma. It occurs enclosed 
within the augite and olivine erystals, and occasionally, in the 
larger felspars. Much of it, however, is scattered through the 
ground mass. I am inclined to think that it may have a patho- 
logical significance, and be a result of alteration in the rock. It 
certainly appears to me that the crystals in which magnetite is 
present are clearer and lighter than those in which none appears. 
There appear to be no cases in which felspar is actually included 
in the augite or olivine, although in some cases felspar and one of 
the other minerals have mutually interfered with one another's 
development. The basalt cannot be considered of the ophitic 
type, but rather of a granulitic character. Professor Judd’ 
considers that the ophitic type of structure is characteristic of 
basalts which have solidified with perfect internal equilibrium, ~ 
while the granulitic type indicates internal movement during 
consolidation. The flow structure being so well shewn in our 
rock, this view of the granulitic structure is confirmed. 
Mr. Curran has had thirty slices cut from the Bald Hills and 
Mount Pleasant basalt, and mentions the localities from which 
his specimens were obtained. My own specimens have been 
obtained from different localities and mainly from those marked 
B, C, D, and E on the map. Locality B, is at the highest 
part of the Bald Hill, near Perth, about seven hundred feet 
above Bathurst. A shallow quarry exists there and the freshest 
' The gabbros, etc., oe a Age in Scotland and Ireland.—Q.J.G. S., 
Vol. xur. (1886), p. 
