NOTES ON A ROCK FROM NEW ZEALAND. 
207 
calculation based on the assumption before referred to, that 
flow of water is nearly proportional to the pressure, shows 
that a head of 100 feet, acting through the same amount of 
rock would yield upwards of 1,250,000 gallons per day. If 
instead of reducing the water level in the well by 11^ feet, 
the head of water in the bed had been increased by a like 
amount, a yield of water only a little less than that actually 
obtained would have resulted, the reduction being due to the 
increased amount of rock through which the water pressure 
would be exerted. The receptive capabilities of such a well 
might fairly be put down at about 1,000,000 gallons per day, 
if the water could be put into it fast enough to maintain a 
head of 100 feet above the rest-level, a result agreeing with 
that arrived at in another way. 
(To be continued.) 
NOTES ON A ROCK FROM NEW ZEALAND, AND ON 
THE DUST EJECTED IN THE ERUPTION OF 
TARAWERA, IN JUNE, 1886.* 
BY THOS. H. WALLER, B.A., B.SC. 
The specimen which forms the subject of the following- 
description was collected by my friend, John H. Lloyd, Esq., 
some three years ago, at Wairoa, on Lake Tarawera. On his 
return to this country he very kindly gave me a slice from it, 
but I found that it was so full of cracks, and, therefore, so 
readily disintegrated that I put it aside despairing of making 
a successful section. When, however, in June of this year 
the great volcanic eruption occurred in New Zealand, and 
buried in the ejected ashes and mud the village of Wairoa, 
the interest added to the specimen mentioned induced me to 
make an attempt to grind it thin. 
Thanks to some practice which I had lately had with 
vesicular and friable rocks I was able to obtain a fair section. 
The specimen is a grey glassy rock with very numerous 
cracks. It shows also many crystals and splierulites, many 
of the latter being hollow. On microscopic examination the 
ground mass is found to be perfectly glassy but to contain a 
very large number of minute crystals of a pale green or 
greenish yellow colour. They are about four to six times as 
long as they are thick and a good proportion of them are 
* Transactions of the Birmingham Natural History and Micro¬ 
scopical Society, Geological Section, October 20th, 1880. 
