BocJy-f< near Heathcote. 3J^i 



the Ordovicians cannot be made out in thn Meld. Under the niici'O- 

 scope (No. G12) (PI. XV., Fig. 2) the bedding planes, defuied in the 

 hand specimen by red band, are seen to consist of iron-stained frag- 

 ments, some of which can be seen to be igneous. The bulk of 

 the rock has been silicified, and in it occur minute rods which 

 may be volcanic glass. Some colourless circular chalcedonic 

 areas may be secondary segregation of silica, but their definite 

 outlines suggest that they are probably organic. The rock aj> 

 pears to have been originally a submarine bedded tuff, or a 

 detrital rock formed from igneous material. The liedded 

 cherts of Lady's Pass are surrounded liy members of the 

 diabase series, some of which are foliated tuffs. The cherts are 

 continuous in strike vrith the foliation of the tuffs, amd the former 

 presence of crystals in the rocks is indicated by the shapes of the 

 hollows left after their removal. Less silicifie'd forms were seen, 

 which approached in character a diabase tuft", and, no doubt, that 

 was their original character. Their relations to the Ordovician 

 rocks, of course, cannot be made out in the field. 



The cherts of the hill south-west of Railway Gate 51 occur 

 between Ordovician shales to the W. and diabase to the east- 

 wards ; but no section showing their relations is to be seen. 

 In places they pass from black bedded and folded cherts into 

 ironstones, and to the east in the shallow railway cutting they 

 can be seen to pass into fragmental diabase. One of the less 

 cherty types (No. 631) shows in section under a high power 

 (l-9in.) a chalcednnic matrix, and scattered through it are 

 aotinolite needles, small rounded shapes, possibly Radiolaria and 

 larger irregular clear cellular masses having a different refractive 

 index from the matrix, which are almost isotropic. Tbey are 

 probably fragrments of cellular volcanic glass, and the rock is a 

 fine basic volcanic ash in which the minutedy fragmental 

 groundmass has been silicified. 



The best field evidence showing the relations of the black 

 cherts to the Ordovician series is to bo seen near Diorite Knolj, 

 S. Heathcote, and at Red Hill. In both localities dips and 

 strikes of the black cherts agree almost precisely with those 

 of the Ordovicians, and less cherty types occur between the 

 two series. Furthermore, no sign of conglomei'ates containing 

 chert fragments occur between the two. The presence oi chert 



