THE VICTORIAN NATURALIST. 65 



a large block of conglomerate may be seen standing on a narrow 

 neck, the softer, gritty rock having been eaten away all round the 

 base. The bed of the creek frequently rises by a vertical step, or 

 up a narrow steep crack along a joint. Sometimes a large pool 

 is formed in the bed of the creek, one noticed being about 30 feet 

 in diameter and about 8 feet deep in the middle. Small ferns in 

 considerable variety occupy any place on the rock where a slight 

 irregularity or hollow enables them to rest, being especially 

 abundant round the edges of these pools. 



In examining the relations of the conglomerate to the other 

 rocks of the vicinity, these may be divided into two — those which 

 were or may have been in existence before it and those of more 

 recent formation. It is evidently from the first of these, or from 

 other deposits now entirely removed or hidden, that the materials 

 of the conglomerate were derived. The pebbles are nearly all 

 waterworn. To transport a rounded stone 2 feet in diameter a 

 current of about ten or twelve miles an hour would be required. 

 Mountain torrents in the Alps are known to attain a velocity of 

 eighteen to twenty miles an hour ; but to give these velocities a 

 steep fall is required, so that the accumulation of any large extent 

 of such conglomerates needs a high range of mountains in the 

 vicinity, which would supply both the materials and the trans- 

 porting power. The conglomerates would then be deposited at 

 the foot of the ranges, the gritty bands and sandstones being 

 formed during times when the flow was slower or in places out of 

 the direct current. They would naturally, as a rule, be nearly 

 horizontal, as any great slope would produce a current sufficient 

 to prevent deposition of the finer materials. 



The underlying rock, wherever I saw it, was Lower Silurian 

 rock, on which the conglomerate rests unconformably. The 

 materials of the conglomerate are such as occur in the Silurian 

 rocks. Though granite and trap rocks occur over large areas 

 now as surface rocks, no pebbles of either seem to occur in the 

 conglomerate, so that they would appear either to be of later 

 origin than" the conglomerates or not exposed on the surface, 

 the part of the range from which the conglomerates were derived 

 consisting of Silurian or similar stratified rocks. I have not yet 

 been able to examine the parts of the conglomerates near the 

 granite and trap sufficiently to ascertain whether they are in any 

 way affected by these rocks. 



Of the more recent formations, the principal one is the 

 occurrence of a few thin quartz veins traversing the con- 

 glomerates, one of which at least is highly mineralized. These 

 veins vary from a quarter of an inch to one inch in thickness, 

 and are vertical, cutting through the individual pebbles of the 

 conglomerate. One of them has a direction of N. 56 W., the 

 others nearly north and south. Veins of quartz also must have 

 existed before the formation Of the conglomerate, in the rocks 



