134 C. A. SUSSMILCH. 
this tuff bed there are numerous rounded masses of rhyolite 
up to 10 feet in diameter, similar in character to that 
described below as outcropping on the Travelling Stock 
Reserve. 
Besides this bed numerous other tuff-beds occur inter- 
stratified with the claystones and limestones. They range 
in thickness from less than an inch up to over 100 feet. 
They are for the most part very fine-grained (Plate 17), light 
in colour, are perfectly stratified, and under the microscope 
are found to consist mainly of fragments of quartz, felspar, 
and minute particles of volcanic glass. 
D. The Rhyolite.—This occurs as a large flow, outcrop- 
ping on the Travelling Stock Reserve (No. 10191), at the 
junction of the Bowan Park and Cargo Roads. 
Petrographical Description.—a. Megascopic Characters. 
Colour, reddish-brown. 
Fracture, even. 
Crystallinity, aphanitic. 
Granularity, porphyritic. 
Minerals visible, felspar. 
b. Microscopic Characters. 
(1. Crystallinity, hypohyaline, (largely glassy) 
2. Fabric, porphyritic, with a groundmass 
largely glassy, but cryptocrystalline 
Tee 2 largely .plagsy, Duties 
| in part and exhibiting perfect flow- 
structure. 
3. Grain-size of the phenocrysts 1°5 mm. 
Minerals present, orthoclase, oligoclase, quartz. 
The thickness of this flow could not be determined, but 
it is not less than 200 feet. Its position at the top of the 
Silurian strata, and the similarity of the rhyolite masses 
included in the red tufis, point to the probability that these 
two formations belong to the same volcanic outburst. 
