284 FOSSILIFEROUS TUFF, ETC., AT CAVAN, 



together with the absence of suitable instruments, etc., I was 

 only able to make a very rough examination of the country as 

 shown on the plan; still I think there is enough detail shown to 

 be a guide to anyone possessing the time and inclination who 

 may feel disposed to thoroughly investigate the surroundings, 

 map out the district on a scientific basis, and so help to clear up 

 the question of the so-called "Passage beds" of the Yass district. 



I have, since writing the above notes, had an opportunity of 

 visiting Melbourne and perusing various reports and papers on 

 the Snowy River porphyries, which are held by the Victorian 

 geologists to be of Lower Devonian age. I was also allowed by 

 the officers of the Geological Survey Department to inspect the 

 collection of rock specimens from the Snowy River district, and 

 found that they were nearly all similar to the rocks which I 

 obtained at Cavan. 



In a paper entitled *' The Physiography of the Australian 

 Alps "(6) Mr. Jas. Stirling, F.G.S., F.L.S., says:— "There is a 

 well marked stratigraphical break between the underlying Silu- 

 rian beds and the lowest members of the Devonian series. The 

 sedimentary rocks of the latter occupy basins in the former^ 

 and are found in isolated areas. The lowest Devonian rocks are 

 certain quartz porphyries, fragmental porphyries, andfelsitic rocks 

 — the products of volcanic activities which marked the close of the 

 Silurian Period. These rocks occupy a large portion of the western 

 watershed of the Snowy River. At several points, notably the 

 Cobberas Mountains, Wombargo Mountains, etc., are very distinct 

 remnants of this period of igneous action; round these centres are 

 grouped beds of consolidated ash and tufa, while resting in hollows 

 in these igneous masses are beds of conglomerate, shale, and crys- 

 talline limestone containing fossils of distinctly Middle Devonian 

 age. Such Middle Devonian areas now form mere pockets in the 

 general land surface, and have suffered extensive denudation. 

 The lithological and palseontological characteristics of 

 the Middle Devonian are as follows : — At Bindi, on the east side 

 of the Tambo, beds of blue crystalline limestone rest on sub- 

 ordinate beds of conglomerate. The limestone beds are inclined 



