Sullivan — On Thenar elite. 
Glacial Period, such as that surmised to have existed iu Middle and 
Western Europe at the commencement of the Human Epoch. 
Without wishing, however, to attach undue importance to the 
astronomical causes just discussed, I desire to direct attention to ano- 
ther kind of evidence of the existence of extreme temperatures, 
rather than of great cold throughout the year in Europe, at a period 
probably coincident with the so-called Glacial Period. This evidence, 
though of special interest in connexion with the astronomical specu- 
lations just noticed, is independent of them, and is of equal value in 
connexion with any other hypotheses that may be proposed to ex- 
plain the causes of the low temperature which undoubtedly did once 
prevail in temperate regions of Europe. 
Our knowledge of crystallo-genesis, and of the conditions under 
which the chemical combinations forming rocks are produced, is as 
yet too limited to help us very much in the great geological problem — 
the determination of the temperature which prevailed under certain 
given circumstances, at any period of geological time. The present 
state of the question as to the genesis of the granitoid and other allied 
rocks, shows how much yet remains to be done before crystallo-genesis 
shall be in a position to supply us with information as to temperature, 
where organic life fails. Wherever crystallo-genesis does give us a 
full answer, the information is usually more definite and precise than 
even that afforded by life. Thus the existence of rhombic crystals of 
sulphur in a fissure or geode is a certain proof that the temperature at 
which the crystals were formed was below 100° Cent. Again, when 
brookite occurs in a rock, we may be sure that after the formation of 
that mineral, the rock had never become heated to a temperature even 
approaching dull redness. And again, the water of crystallization of 
gypsum is certain evidence that that mineral was formed at tempera- 
tures below 360° Cent. The evidence of the existence of extreme 
temperatures at a former geological time, to which I desire to draw 
attention, is of an analogous kind. 
When disodic sulphate crystallizes at temperatures below 35° 
Cent., it takes up ten molecules of water, and forms glauber salt ; 
above 35° it crystallizes as an anhydrous salt. Both salts occur in 
nature — the hydrated salt as sulphate of soda, or mirabilite ; and the 
anhydrous salt, as thenardite. The hydrated salt must have been 
formed from cold solutions, or at least from solutions which were 
under 35° Cent, when the crystals were formed. Thenardite, on the 
other hand, must have been formed in solutions above 35° Cent. Until 
very recently thenardite was a rare mineral, having been noticed only 
in certain springs near Aranjuez, in Spain, where it was discovered in 
process of formation ; in the salt-beds of Ocaiia in the same district ; and, 
lastly, in the salinas of Chili, accompanied by a mineral called giau- 
berite, consisting of a combination of anhydrous calcic and sodic sul- 
phates, or, in other words, thenardite and anhydrite. Within the 
last few years great deposits of thenardite and glauberite have been 
