344 N. E. Junner: 



Tlie dyke outcrops on the surface just to the west of the mine, 

 and some good sections showing the various rehitions of the dyke 

 breccia and sihiriaii are seen in shallow workings in the dvke. 



(1)) The breccia and crush conglomerate. 



Tliis interesting feature was first examined in numerous woi-kings 

 along the line of the dyke below the mine, and north of the Diamond 

 Creek. Numerous pebbles, set in a very fine matrix, frequently 

 occur in the silurian alongside the dyke. At first sight this might 

 be mistaken for a sedimentary conglomerate, but a little considera- 

 tion shows that it is a fault conglomerate, and not a sedimentary 

 one. In the first place all the pebbles consist of similar sandstone, 

 shale and quartzite to the adjacent wall rock. Secondly, on the 

 surface this conglomerate has been seen alongside the dyke at places 

 over half a mile apart. Now the strike of the dyke is approxi- 

 mately north and south, while that of the silurian is about north 

 2U deg. east. Hence it will be seen that the conglomerate is not 

 bedded, and cannot therefore be a clastic conglomerate. Thirdly, 

 when examined in tiie mine, sections frequently show the junction 

 of the normally dipping silurian with the breccia and dyke, and it is 

 seen tiiat brecciatitm occurs in a zone roughly parallel to the walls 

 of the dyke. Also in some cases a passage from a breccia into a 

 breccia conglomerate and crush conglomerate is noticeable, 

 l^ourthly, the cobljlcs sliuw certain 2:)eculiarities, such as diiupling, 

 plane surfaces where the cobbles have rubbed against one another 

 flattening and twisting. The fault origin appears therefore to be 

 clearly establislicd. Considerable variation in the size of the cobbles 

 has been noted. The average size is two or three inches in dianietei-, 

 while one extreme example was over two feet long, and nion- than 

 fourteen inches' in diaiiictiT. WIkmi the fragnie!its aie angular and 

 sub-angular the rock is called a crush breccia. Further rolling 

 and crushing of the |)i'l)bles rounds oft" the angles and forms a crush 

 conglonierati'. Mr. Dininl mentions the oeeurrt'iiee of the breccia 

 on only one wall ol' the dyke. The writer, however, has seen that at 

 the mine and elsewliere the breccia t i-ei|ueiit ly occurs on lioth walls. 

 Tins fault zone has acted as a plane of weakness, thrinigh which the 

 dyke has In-en intruded. Horses of breeciated-niateiial and fault 

 cobbles ai-i; frecpiently found well within the dyke; in one case in 

 the 300 feet level fault cobbles were seen as much as six 

 feet within it. The dyke occasionally wanders from the zone 



1 K. .1 Diimi Oji. cit. 



