494 PETROLOGICAL ABSTRACTS AND REVIEWS 



basic rocks. The sedimentary formations, which prior to the folding 

 had a thickness of over 30,000 feet, are described, and a list is given of 

 the fossils found. 



The igneous history begins in Lower Devonian times with the 

 extrusion of spilitic lavas and tuffs. In the Middle Devonian similar 

 rocks attain a thickness of over 7,000 feet, and associated with them are 

 2,000 to 3,000 feet of intrusive dolerite, in many cases albitized. In 

 Upper Devonian times some 3,000 feet of agglomerates were formed, 

 and, after a long period of quiet, rhyolites, andesites, and tuffs appeared 

 in the Lower Carboniferous. The intrusion of the peridotites then 

 followed, chiefly along the fault line previously mentioned, and probably 

 during the crust-movement at the close of the Carboniferous. Gabbros 

 and eucrites came later than the serpentine, and cutting these are dikes 

 of dolerite. From latest Carboniferous to early Mesozoic times came 

 a long series of granitic intrusions consisting of granodiorites and por- 

 phyries, and titanite-, tourmaline-, and other granites. Besides these 

 rocks there are numerous lamprophyres whose time period was not 

 determined. Following the Permo-Carboniferous was an era of great 

 crumpling, then followed a long period of erosion which exposed the 

 granite, and then a later period of sedimentation. During Tertiary 

 times the formations were largely volcanic, and thick flows of basalt 

 occurred. A great period of elevation and block-faulting closed the 

 Tertiary. 



The second paper deals with the geology of the Nundle District, 

 and the third with the petrology of the entire region. Various rocks are 

 described: spilites, used in the sense of Dewey and Flett for lavas with 

 sodic feldspars, contain acid oligoclase and augite with some secondary 

 chlorite and epidote and with or without magnetite; the so-called 

 " keratophyres " are composed almost entirely of acid oligoclase with some 

 interstitial chlorite from augite; the dolerites consist of plagioclase 

 (andesine to albite), augite, magnetite, with a little quartz and various 

 accessories, and are medium-grained. The term dolerite is apparently 

 used in a different sense from that common in the United States, 

 where it signifies a coarse-grained basalt containing a basic plagioclase. 

 The writer speaks of albitization proceeding inward in the feldspars, 

 by which he means, apparently, that the sodic rims are secondary. It 

 would seem more probable that the zonal rims are primary. The rock 

 thus appears to be an augite-andesite. The peridotites are chiefly 

 harzburgites, but there are local occurrences of dunite and lherzolite. 

 With the absence of olivine, enstatolites occur. Associated with the 



