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



a breccia of red and white limestone. The fauna of this lime- 

 stone has been tabulated above. 



Directly east of the Nemingha limestone zone is the largest 

 mass of porphyritic spilite that occurs in the district; it forms 

 the ridge termed East Gap Hill. This, also, must be correlated 

 with the Tintinhull spilite. The southern end of the hill consists 

 of pyroclastic rocks, with the seemingly massive, ferruginous 

 keratophy re-breccia like that on West Gap Hill. This passes 

 without any junction-line into a very vesicular porphyrite, and, 

 on the top of the ridge, into a slightly vesicular porphyrite, with 

 phenocrysts of albite, and a subvariolitic groundmass of felspar, 

 uralite, and chlorite (see Text-tig. 4, p. 565). Except for the 

 greater abundance of the felspar, the mineral-composition is 

 exactly that of the spilites of Tintinhull, and there is little reason 

 to doubt that this is but a thicker, and more coarsely crystalline 

 portion of the same mass as the other rocks, brought by faulting 

 or folding into its present position. The northern end of East 

 Gap Hill is occupied by a mass of rather decomposed dolerite, 

 which invades the spilite-porphyrite, and extends nearly to the 

 Cockburn River. This intrusion is partly albitic, but the greater 

 portion contains andesine, or labradorite. We will return sub- 

 sequently to discuss the manner of origin of the igneous rocks 

 of East Gap Hill(p.564). 



Eastwards of this occurrence of the Igneous Zone, we can not 

 determine the tectonic structure with any degree of probability. 

 No further zones of igneous rock occur, which resemble either 

 the spilite-porphyrite, or the ferruginous keratophyre-breccias 

 described above. Moreover, the angles of dip of the strata, when 

 observable (and this is but seldom), afford no help, being usually 

 almost vertical. However, the large mass of limestone in por- 

 tion 91 and the eastern end of 88, though too altered for the 

 preservation of fossils, resembles that of the horizon last de- 

 scribed, and may be supposed to be the limestone that should 

 occur below the spilite-porphyrite of the Igneous Zone on East 

 Gap Hill. Isolated lenticles of limestone occur on the same 

 horizon in portion 168, and are included in a mass of tuif-breccia 

 in portion 207, while a possible continuation of this zone is shown 



