The Geology of the Loiver Le'ujh Valley. 95 



feet, and in one or two other sections 50 feet thick. Our former 

 estimate of 95 feet for its thickness at the cemetery section is 

 probably too great. There is no certainty that it reaches much 

 higher up the hill than the site of the quarry, viz., 110 feet. 

 It appears, however, to descend here to a somewhat lower level 

 than usual on the bank. 



We have already noted the height of the lava at the most 

 prominent outcrops. The level of the river close to the elevation 

 to be measured has in each case been taken as the best available 

 zero point for aneroid work. Allowance has then to be made for 

 the fall in the country as the river is followed down. For 

 example, the water-level at Bull Island we found so be 80 feet 

 above that at Shelford Bridge. By taking this into account, we 

 estimate that the summit of the lower basalt at its southern 

 extremity is fully 100 feet below the outcrop on Dog Island. 



When speaking in our former paper of the basalt on the Leigh 

 banks, we expressed the opinion that it could not be younger 

 than miocene. This statement, however, is only correct in 

 reference to the earlier flow. The upper one, which caps the 

 miocene conglomerate, and covers the western plains, is much 

 later, and may be pliocene or post-pliocene. 



We could observe no difference in the external appearance of 

 the rocks from the respective flows. Both are highly vesicular 

 not only on the surface, but also for some depth down. The 

 quarrymen tell us that the lower basalt is tougher and more 

 dilflcult to crack for road metal than the upper. Possibly a 

 microscopic analysis might disclose some variation in their 

 mineral constituents. 



By Messrs. Etheridge and Murray, the source of the newer 

 basalt on the right bank of the Leigh is considered to be Mount 

 Mercer, which is 17 miles north of Shelford. For that in the 

 immediate neighbourhood of the township, we think that Gow's 

 Hill, a point of eruption about 6 miles to the west, must be 

 credited with having contributed at least a large portion ; it is 

 indeed not unlikely that the flow from the former vent was 

 joined by one from the latter. In their essay, the authors named 

 describe the courses of several distinct flows of the later basalt, 

 some of which they trace down to and beyond the Dog Rocks. 

 It is probable that a further study of these in the field will throw 

 light on some of the questions raised in the present paper. 



