Tlie Geology of Coimdidai. 65 



ferruginous cementing material appears to be often i-eplaced by 

 silica, and all the harder cemented rocks seem to have the form 

 of lenticular sheets, varying much in extent. On the other side 

 of this hill, remote from the quarries and close to the Melton 

 Road, an outcrop of limestone is seen in a small gully ; it is 

 overlain by ferruginous rocks, and has an apparent dip in a 

 north-easterly direction. Along the road from Coimaidai to the 

 Bullengarook Road outcrops of sandstone, gravel and conglomerate 

 occur ; the topmost beds, which lie directly under the basalt, are 

 about 240 feet above the base of the quarries. Jt is thus seen 

 that, in the vicinity of Coimaidai, the limestone is overlain by 

 series of sands, gravels, quartzites and conglomerates, the bed 

 superposed on the limestone being dilferent in ditFerent places. 

 That the limestone of the quarries is older than the associated 

 beds, and does not occupy a valley of erosion in them, is clear to 

 the writers from the following considerations : — 



(1) Its apparent position with regard to the overlying 



beds. 



(2) The absence of either rounded or unrounded fragments 



of grit, quartzite, or conglomerate in the limestone, 



or gravels intercalated with the limestones in the 



quarries. 



It is indeed fortunate that the evidence on this point is clear 



so far as the quarry limestones are concerned, as in other parts 



of the district the relation of the limestone to the other beds is 



inverted ; for instance, at a point about two and a half miles 



below Coimaidai, on the west side of the Pyrete valley, a section 



is exposed in which we find in descending order : — 



(1) Basalt. 



(2) Limestone, containing abundant freshwater shell casts, 



which, in the opinion of Mr. 0. Hedley, F.L.S., 

 are mostly of the genus Limnaaa. One Bulimus 

 was found. 



(3) Clay, sand, gravel and conglomerate, merging into 



quartzite. 



About a quarter of a mile higher up the quartzite is well 

 developed and rests directly on the Silurian rocks. 



The limestone in the above section is essentially of the same 

 composition as the quarry limestone, being mainly carbonate of 



