Dr Hamilton on the Mme of Corundum in Singraula, 307 
nor is there any reason to suppose, that the three kinds thus 
distinguished by some of the mineralogists, correspond at all 
with the three kinds acknowledged by the Indian artificers. 
I have, however, little doubt, that a proper examination of nu- 
merous specimens would enable a judicious mineralogist to di- 
vide corundum into several species, possessed of peculiar quali- 
ties to suit each for some useful purpose, and not founded on 
hypothetical conjectures respecting their formation, or trifling 
variations of appearance, which are only worthy of notice, so far 
as they may enable us to distinguish the substance from others 
of a different nature, and the various useful species from each 
other. 
Art. XVII . — Account of Rocks formed hy Hot-Springs^ Tor- 
rents of Hot Water, bursting of Subterranean Lakes, Air- 
Volcanoes, and Cold-Springs. By Professor Jamesok^. 
1. Rocks formed from the Water of Hot-Spfings. 
VIany of the more observing and intelligent of the inhabi- 
tants of Iceland believe, that certain rocks in their country have 
been formed by deposition from the water of hot-springs. This 
opinion, which at first sight appears very improbable, was 
adopted by the travellers Olafsen and Povelsen, who were 
several years occupied in examining the natural history of that 
remarkable island, and who describe whole mountains as having 
been formed by hot-springs. And, very lately, M. Menge, as 
stated in the last Number of our Journal, returned from 
Iceland fully convinced, that very extensive formations of ther- 
mal rocks extend throughout that extraordinary country. As we 
consider this fact one of great geological importance, we shall 
now lay before our readers some account of the observations of 
Olafsen and Povelsen and Menge, and accompany it with occa- 
sional remarks. 
In the Borgarfiord district, in southern Iceland, there is a 
striking and lofty mountain named Baula, of a white colour, 
and of a rather irregular structure. Nearly the whole mass, 
from its base to its summit, as determined by numerous natu- 
Read before the Wernerian Natural History Society, 12th February 1820. 
