72 MINERALOGY AND GEOLOGY. 
stalline and gives out great heat.* When glass is raised to a certain 
temperature, and by its maintenance is preserved in a soft state, it 
does the same. 
In sulphur, phosphorus, and selenium, therefore, the fluid state 
below the temperature of solidification—the intermediate condition 
between fluidity and solidity—the viscid state long retained—the 
solid state of selenium which evolves heat on erystallizing—all 
appears to be homologues, at once, of liquid water below 32°, and of 
the glassy state of matter. 
Should this hypothesis be verified, water below 32°, or rather, per- 
haps, from the temperature of maximum density downwards through 
that of freezing, may have to be regarded as the type of the vitreous 
condition of matter; and the causes of the peculiar characters of 
that condition, its effects on the transmission of the vibrations of 
sound and light, the conchoidal fracture, &c., may have to be dis- 
covered by researches on its molecular nature. » 
SCIENTIFIC AND LITERARY NOTES. 
MINERALOGY AND GEOLOGY. 
TABLES FOR CALCULATING THE THIOKNESS, ETC.,, OF INCLINED STRATA, 
In our last series of Notes (Vol. V., p. 544,) we gave a method of calculating 
approximately the thickness of inclined strata when the dip does not exceed five 
degrees. The annexed Tables were drawn up to accompany the note in question, 
but were omitted from want of space. The angles of dip from 1° to 89° are con- 
tained in column A, The second column, B, shows the thickness in feet, corres- 
* These properties of selenium are here stated on the authority of Hittorff, cited in 
Graham’s “ Elements of Chemistry,” second edition, vol. ii. pp. 688, 689. 
The case of vanadic acid strongly resembles that of selenium, but extends thig series of 
concurrent phenomena to a range of temperatures nearly approaching those which govern 
the molecular changes of glass. It fuses at a red heat, and crystallizes on cooling, but 
remains fluid below its freezing-point. At the moment solidification commences, it agaim 
becomes red-hot, and remains so as long as crystallization continues. 
The crystallization of glass, it has been seen, takes place at a high temperature, from the 
ordinary state of solidity, heat being evolved. So the glassy varieties of gadolinite (like 
glass, a silicate with a compound base), when its temperature is elevated above redness, 
remains solid, but evolves heat (becoming incandescent), and crystallizes: while the erys- 
talline variety merely fuses and intumesces when similarly treated. 
+ The words “ when the dip does not exceed 5°", were accidentally omitted in the note 
referred to. The reader is therefore requested to insert them after the word“ strata” in 
the first line. (vol. v-, page 544.) 
