664 GREAT SERPENTINE BELT OP NEW SOUTH WALES, iii., 



freedom from secondary silicates, and frequently non-amygdaloi- 

 dal character remove them entirely from the group of spilites as 

 recognised by Brongniart. The major primary characters, and not 

 the accidental secondary features, are surely those of specific value. 

 The name spilite, therefore, is applied to them, but in the hope that 

 a better one will eventually be adopted.* 



The spilites are extremely abundant in the lower portion of the 

 Devonian System. They form several important flows in the 

 Woolomin and Tamworth Series, and occur interstratified in the 

 Baldwin agglomerate. The breccias of the Tamworth Series, and 

 the above agglomerate, are largely made up of fragments of spilite, 

 and in the latter it is often very pumiceous. In hand-specimen, 

 they are more or less vesicular, but rarely amygdaloidal. Very 

 frequently they are quite compact, and sometimes resemble a dark 

 green hornfels. The grain-size is usually small, and even, but 

 porphyritic examples are not infrequent. About two dozen speci- 

 mens have been sliced. The texture varies considerably; usually 

 it is pilotaxitic, and exceedingly finely crystallised ; often it is more 

 coarsely grained, with more or less variolitic character. Again, it 

 may approach the granular structure of some basalts. 



The least altered specimen [N.T., 415*] occurs on the French 

 man's Spur, near Nundle. It is rather less finely grained than 

 usual, and has a granulitic to sub-variolitic ground-mass, with an 

 occasional idiomorphic crystal of augite (Plate xxv., fig.l). The 

 felspar is primary acid oligoclase; the augite is but slightly decom- 

 posed, with production of chlorite and epidote. In chemical com- 

 position (see Table i., p. 704), this rock is quite analogous to the 

 Cornish spilites described by Messrs. Dewey and Flett. 



* Messrs. Dewey and Fletts' use of the term Spilitic Suite is even less 

 justifiable. Surely a group of rocks embracing picrites, dolerites, soda- 

 porphyries, and keratophyres is not well described as the "altered basic 

 lava suite. ,: I understand that these authors have, in preparation, an 

 extensive memoir on these rocks, and I trust they will take the oppor- 

 tunity of reconsidering their nomenclature before establishing more firmly 

 such inappropriate terms. 



t These numbers refer to specimens in the Mining Museum, Sydney 

 Duplicates of nearly all the slides specially mentioned here, have been 

 deposited in the Sedgwick Museum, Cambridge. 



