116 Professor How on Natro-boro-calcite, &c. 
Owing to their excessive thinness I could not say whether they 
could be called right or oblique rhombic prisms ; I suspect the latter 
from analogy. By care the ‘ Tiza’ (Natro-boro-calcite) can be 
shown to consist of very fine prisms, sharp, angular, and long, but 
too fine for me to state their form. The diameter was less than 
‘00118 of an English inch. The long prismatic needles of the Tiza 
are in great contrast to the broad tables of the recent mineral in 
your last letter ; of that the plates are about ‘0048 of an inch from 
side to side, but some are a little larger, others a little smaller. In 
some you see regular cleavage—that is, a small rhomb chipped out 
of one side. As far as form goes, therefore, it would seem to be a 
distinct and definite species. I presume it was formed in a dry 
place, for the angles were quite sharp. The connection between 
these borates and sulphates of lime and sulphate of soda is very 
curious.” 
I may state that I had subsequently the opportunity of appre- 
ciating the great accuracy of this description of the appearance of the 
two minerals. 
Arguing from the chemical composition, which, however, may 
not be quite established, and the crystalline structure, I conceive the 
mineral in question to constitute a new species, and I propose for it 
the name of Cryptomorphite (xgurros occultus, and wogpn forma), in 
allusion to its microscopic crystalline structure. 
The truth of the last sentence in Professor Robb’s letter is very. 
apparent. In my former paper on the subject, I adverted to the 
existence of Natro-boro-calcite in the gypsum here, as confirming 
Dawson’s theory of the origin of the rock from the action of volcanic 
waters on carbonate of lime. It is interesting to observe that 
Bechi* found the same (?) mineral, with other borates, in the 
lagoons of Tuscany. The hydrated condition of both the borates 
found here, and of the associated sulphate of soda, shows the action — 
of water; but that of ordinary sea-water would not account for the — 
presence of boracic acid. As regards the soda, the sulphate and — 
borate of lime were probably the substances originally present, and 
chloride of sodium in water being introduced might remove part of 
the calcium as chloride, and furnish borate and sulphate of soda. 
It is confirmatory of this view that a small quantity of rock-salt in 
crystalline grains has recently been found in the gypsum. | 
* Dana’s Min., 4th ed., pp. 394, 395. 
