486 H. S. JEVONS, H. I. JENSEN, T. G. TAYLOR AND C. A. SUSSMILOH. 



the magma in this case assimilated more of the shale than 

 did that of specimen L. No biotite is present, and this is 

 evidence that it is not a product of chemical interaction 

 but an original constituent of the whole magma. The 

 calcite, with probably some dolomite, is most abundant, 

 and occurs both in veins and throughout the rock, replacing 

 different minerals, but notably olivine. The replacement 

 of olivine by calcite or dolomite is common in decomposed 

 basalts of the Sydney district (e.g. those of Hornsby and 

 Guildford), and is no doubt due to decomposition of the rock 

 by percolating water, probably charged with calcium car- 

 bonate from the adjoining somewhat calcareous shale. 

 Whether any of the calcite in specimen M was derived from 

 the shale prior to consolidation, and either remained as 

 unabsorbed grains or was in small quantity dissolved in the 

 watery magma at great pressure and then crystallised out, 

 is a question which it is impossible to answer, owing to the 

 undoubted secondary replacement having effaced the 

 necessary criteria. 



Specimen P. 

 Locality. Taken from the ledge separating the shallower 

 from the deeper part of the Emu Quarry, a few metres 

 from the eastern wall of the quarry. The rock immediately 

 over it has been removed, but, assuming that the junction 

 with the shale extended horizontally from the nearest point 

 where it now exists, specimen P must have lain about seven 

 metres (23 feet) below the surface of the ground, and nearly 

 five metres (16 feet) below the junction with the shale. 

 Below the compact pallio-essexite is a layer of dark fine 

 grained essexite 3J metres (nearly 12 feet)' thick, and 

 below this a band about 20 cm. (8 ins.) thick, richer in 

 biotite and ilmenite, from which specimen P was taken. 

 Underlying this band, whose characters are now to be 

 described, is an aplitic sheet 5 cm. (2 ins.) thick of the 

 kind to be described in the third part of this paper. 





