Reports & Proceedings — Geological Society of London. 283 



can be formulated, the different horizons are readily recognizable by 

 their assemblage of fossils. 



The chemical and microscopic structure of the rocks is dealt with, 

 and the conditions of deposition and stratigraphical relationship of 

 the different members of the series are discussed. In addition, some 

 peculiar structures from the Chipping Norton Limestone are described, 

 and the author adduces his reasons for considering them to be 

 annelid tubes. 



A complete list of the fossils is appended, showing the horizons and 

 exposures from which they have been obtained ; tables giving the 

 correlation between different exposures are also added. 



2. "On the Petrology of the Kalgoorlie Goldfield (Western 

 Australia)." By James Allen Thomson, M.A., D.Sc, F.G.S. 



The district described comprises an area about four miles long by 

 one mile in breadth. Towards its southern end the auriferous lodes 

 are very rich (The Golden Mile), but in the northern end they are 

 not so productive. The information as to the geological structure 

 has mostly been obtained from mining plans, shafts, and workings. 

 The rocks have a general north-north-westerly strike, and most of 

 the junctions are faulted. In " The Golden Mile " the central feature 

 is a boss or broad dyke of quartz-dolerite, which forms a prominent 

 ridge flanked by amphibolites and greenstones. The quartz-dolerite 

 is cut by dykes of albite-porphyry, and west of the main ridge 

 similar porphyries are frequent. Gold is found principally in shear- 

 zones, impregnated with sulphides and tellurides, and is most 

 abundant in the lodes of the quartz-dolerite. 



The rocks for purposes of description are divided into — 



(A) Sedimentary. — Of these the most distinctive are conglomerates and grits, 

 the former containing pebbles of quartzite and of albite-porphyry. 



(B) Igneous. — These are often very highly altered by metamorphism 

 (inducing schistosity and partial reciystallization) and by metasomatic action. 

 They include — - 



(1) Fine-grained amphibolites ; altered basic igneous rocks — probably lavas 



and tufts. 



(2) Fine-grained greenstones ; slightly schistose aggregates, probably related 



to the fine-grained amphibolites in origin. 



(3) ' Calc-schists ' : whitish-green rocks, which are closely connected with 



the greenstones and merge into them. 



(4) Peridotites, serpentines, etc., often filled with carbonates, but perhaps 



comprising originally enstatite-peridotites as well as other types. 

 These rocks form the eastern part of the northern end, and include 

 talc-magnesite rocks and fuchsite-magnesite rocks. 



(5) Hornblende-rocks or pyroxene-amphibolites, probably occurring as dykes 



in the peridotites. 



(6) Lustre-mottled amphibolites, containing remains of felspar, and originally 



hornblende-dolerites. 



(7) Epidiorites, uralitized and saussuritized gabbros or ophitic dolerites, not 



very numerous. 



(8) Quartz-dolerites and their derivatives — amphibolites usually coarse- 



grained, with a considerable amount of interstitial micropegmatite.^ 

 This is the important rock of ' The Golden Mile ' . It contains very 

 coarse pegmatitic veins, and is often to a great extent albitized. It 

 presents a great variety of types due to different stages and kinds of 

 alteration, and many of these phases are difficult to recognize as 

 derived from the quartz-dolerites. 



