Igneous Pebbles. 287 



it consisted of sub-angular and rounded fragments of quartzite, 

 decomposed diorite, limestone, etc., in a dark-coloured siliceous 

 matrix in part calcareous, and was associated with a decomposed 

 dyke and a belt of limestone. He concluded from the following: 

 evidence : — 



(a) The direct association of the breccia with the decom- 

 posed dyke; 



(b) The appearance of presumably the same belt of breccia 

 and dyke, first, on one side of the limestone, and then 

 on the other; 



(c) The occurrence of included fragments of limestone in 

 the breccia ; 



that the breccia was probably of volcanic origin, occupying an 

 immense strike fault in the silurian rocks. 



In 1901. Mr. H. Herman^ described in some detail the relations 

 l^etween the beds near the Thomson river. He states that " A 

 gradual transition in texture can be traced from the coarse fossili- 

 ferous conglomerate . . . through fossiliferous shales with 

 crinoid stems, to highly calcareous encrinital shales, and finally 

 to encrinital limestone or marble." He regarded the conglomerate 

 as a normal shore line deposit, and explained the presence of 

 limestone pebbles in it, as either due to contemporaneous erosion 

 or thouglit possibly that they may have been derived from a pre- 

 existing formation. Mr. F. Chapman^, in 1907, described the 

 fossils occurring in the limestone near the Thomson River copper 

 mine. He mentioned the occurrence of flakes of biotite and 

 chlorite, and contorted bands of tuffaceous andesitic ejectmenta, 

 in sections of the limestone, and suggested that volcanic activity 

 took place contemporaneously with the deposition of the limestone. 



Field Relations neap the Thomson River, Walhalla. 



The Silurian sediments near Walhalla ^ consist lithologically of 

 sandstones, shales and slates, for the major part, but lenticular 

 bands of limestone associated with gritty and conglomeratic beds 

 are not unusual. The structure is geosynclinal with thin bedded, 

 highly cleaved, shales and slates in the centre of the geosyncline, 

 and more coarsely grained sandstones and gritty beds towards 

 the margins. 



1 Op. cit., p. 12. 



2 "The fossiliferous limestones and cong:lonierates of the Thomson and Tveis rivers and Marble- 

 creek, Gippslaiid." Records Vict. Geol. Surv., vol. ii., pt. 1. 



3 For geological map and sections of the locality dealt with, vide Herman, op. cit. 



