166 GREAT SERPENTINE BELT OF NEW SOUTH WALES, iv., 



movement: therefore, the magma must have come near to the 

 surface (the sea-bottom), during the period of deposition. The 

 more deep-seated magma (the dolerites), encountered consolidated 

 sediment, and have rough, shattered lines of contact with the 

 rocks they invade. The keratophyres, in particular, must have 

 formed at some depth, and only after the complete consolidation 

 and some faulting of the specimens. But the stratigraphical 

 record shows that there was no important faulting or folding 

 from Middle Devonian to Lower Carboniferous times, and we 

 must accordingly consider these faults as merely local movements 

 around the centres of Middle Devonian, submarine, igneous 

 activity. 



The discovery of the agglomeratic keratophyre, between Silver 

 Gully and Pipeclay Creek, throws some doubt on the former 

 assumption of a single ejectamental origin of the "tuffs," "brec- 

 cias," and "agglomerates" of the Devonian stratigraphical suc- 

 cession. When first these rocks were discovered in the Tamworth 

 district, they were considered as sills by Professor David(38), 

 though later, upon the evidence of their microscopic structure, 

 he stated that they were tuffs, and termed "intrusive tuffs" 

 certain occurrences in which the relation of the igneous to the 

 sedimentary rock seemed to be an intrusive one. More recently, 

 the so-called tuffs in the Silurian Series, east of the Jenolan 

 Caves, have been proved by Mr. Siissinilch to be really strongly 

 differentiated, intrusive porphyries full of inclusions, not only of 

 cognate igneous rocks, but of fossiliferous limestone, and the 

 enclosing cherts and slates. The writer has seen these, under 

 Mr. Siissmilch's guidance, and has noticed some analogy (first 

 suggested to him by Professor David) between them and the 

 agglomeratic rocks of the Tamworth Series. This analogy does 

 not amount to a parallelism, however. In an earlier communica- 

 tion, the writer suggested that the apparently intrusive character 

 of the acid tuffs into the Devonian chert might be due to the 

 drying and cracking effect of hot ash falling on to damp mud 

 Other exposures have now been found, in which this explanation 

 is inapplicable. In Swamp Creek, for instance, is a mass of acid 

 ianeous rock, resembling svhat has been termed "acid tuff," but 



