400 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 7, 



but the limestone also has undergone the same change. In close 

 connexion with the silicified rocks are found over a vast area brec- 

 ciated rocks, either assuming the character of siliceous-slate-breccia, 

 or of a compound of dioritic and siliceous rock, approaching on one 

 side to diorite, on the other to siliceous slate. The limestone in the 

 same region is also commonly brecciated, containing angular frag- 

 mentary particles and masses of siliceous rock, which increase some- 

 times in such a degree as to supplant the limestone in part or com- 

 pletely. Hence one and the same bed of limestone may be found in 

 one place pure, further on passing into a brecciated limestone with 

 fragments of siliceous rock, and still further into a siliceous breccia 

 with enclosed fragments of limestone, which diminish at a greater 

 distance, and even disappear altogether, when there only appears a 

 siliceous breccia containing more or less calcareous matter. The 

 fragments of limestone in the siliceous breccia are highly crystalline, 

 and all traces of fossils are generally wanting. 



Associated with the silicified slate quartzose hornblendic rock 

 occurs to a great extent. Near granite a metamorphic rock re- 

 sembling gneiss and mica-schist has been observed in a limited 

 area. 



The silicification seems to be most developed near the serpentine, 

 the altered rock being there in a great measure intersected by quartz 

 veins, or so highly charged with silex, that layers of pure quartz 

 appear interlaminated with the silicified slate. Also near serpentine 

 cavernous chalcedonic masses occur, and opal. 



There can be little doubt, that the igneous rocks were intruded when 

 the slaty rocks and limestone were just in the process of being formed, 

 and the two masses have influenced each other in their composition. 

 Even the igneous rocks, syenite, diorite, and porphyry, are much 

 more overcharged with siliceous matter than I ever before had the 

 opportunity of observing. The brecciated rocks, so extensively dis- 

 tributed, show equally the mutual influence of igneous and sedi- 

 mentary rocks. The silicified slates are sometimes much contorted 

 and twisted, especially near serpentine. 



The breccia passes sometimes, but not commonly, into conglo- 

 merates with rounded particles of rock, which, however, are to be 

 distinguished from the superficial conglomerates, composed of con- 

 solidated drift of more or less recent date. 



At a greater distance from the Dividing Range and the high spurs 

 which descend from it, and which for the most part diminish rapidly 

 in height, there occurs a great extent of soft slate, interstratified 

 with more compact beds, from half an inch to several feet in thick- 

 ness, and charged, as it appears, with dioritic and siliceous matter, 

 but rarely assuming the character of grits or sandstone. True 

 diorite is also observed interstratified with slate, sending out in some 

 cases veins into the latter rock, and causing a silicification of the 

 nearest layers to a small distance. In the same manner felspar- 

 porphyry (felsit-porphyr) and syenite occur also in beds in the 

 slate, without visibly disturbing the latter. Brecciated rock appears 

 in large layers near the Dividing Range, but these are more rarely 



