566 GREAT SERPENTINE-BELT OF NEW SOUTH WALES, V., 



are described in detail in a later portion of this paper. The 

 relation of these breccias to the overlying sediments is obscured 

 by drift. The Nemingha limestones follow immediately west of 

 the hill, but are believed to be separated from the igneous rocks 

 of East Gap Hill by faulting. They show no sign of contact- 

 alteration, and there is other evidence of the presence of one or 

 more strike-faults running through the Gap itself, e.g., in the 

 presence of a fault and a band of fault-breccia traversing the 

 limestone in the "red marble" quarry in Portion 134. The- 

 problem is rendered more complex by the presence of tuffs in 

 intimate association with the limestone, which often cannot be 

 distinguished from those that occur in the Igneous Zone and lie 

 stratigraphically several hundred feet above the limestone. 



The igneous rocks of West Gap Hill are almost entirely f rag- 

 mental. They are quite similar to those of East Gap Hill, of 

 which they are, it is believed, the faulted equivalent They are 

 sometimes very coarsely granular, the fragments being several 

 inches in length, and include cherts and limestones, as well as 

 igneous rocks. The cherts form particularly large angular pieces. 

 This mass of fragraental rock is invaded by massive albite- 

 dolerite, which occurs on the southern end of the hill. Various 

 exposures show the relation of the pyroclastic and sedimentary 

 rocks to one another, and the frequently intrusive nature of the 

 former can be thoroughly substantiated. No single specimen, 

 however, is more instructive than that shown in Text-fig. 5, and 

 Plate liii., fig. 10. This consists of green banded chert, with 

 intercalated bands of purplish pyroclastic material, which have 

 a sharply marked boundary on the one side against the chert, 

 and a gradual passage between the two rocks on the other. This 

 is clearly due to successive small eruptions of tuff, which filled 

 the sea with fine ash, that deposited in layers at first sharply 

 distinct from the clay on to which it fell, but faded away 

 gradually upwards, as the slowly settling remnants of the ashy 

 material became more and more mixed with the normal sediment 

 (radiolarian clay). Intrusive into this banded rock, and cutting 

 across its bedding-plane, is a tongue of breccia, of the same com- 

 position as the interbedded tuff", though of larger grain-size. 



