TRANSACTIONS OF SECTION C. 815 
5. On the Origin of the Saline Inclusions in the Crystalline Rocks of Dartmoor. 
By A. R. Hunt, W.A., £.G.S8. 
The author stated that he had examined 24 sections of crystalline rocks and 
quartz veins connected with the granite of Dartmoor, and found them all to 
contain without exception fluid inclusions with cubic crystals. That the cubic 
crystals in the Dartmoor granites indicate, to some extent at least, chloride of 
sodium seems hardly open to doubt, as the inclusions are exactly like those figured 
by Dr. Sorby from Cornwall, which proved on analysis to contain that salt. 
There are four classes of rock in which these saline inclusions occur, viz. : 
(1) The ordinary porphyritic granite of Dartmoor. 
(2) Eruptive veins of fine-grained granite traversing the main mass and the 
adjacent sedimentary rocks. 
(8) Quartz-tourmaline-felspar veins of aqueous origin, also traversing the 
main mass and adjacent sedimentaries. 
(4) Veins of pure quartz in the culm slates. 
A quartz crystal about one-thirtieth of an inch in diameter in one of the 
aqueous veins contains six different sorts of inclusions, viz, : 
(1) Trregular cavities with both cubic crystal and bubbie. 
(2) Irregular cavities with cubic crystal alone. 
(8) Irregular cavities with bubble alone. 
The same three varieties occur as negative hexagons, making six altogether. 
The bubbles vary greatly in relative size and activity. In the case under 
discussion variation cannot be explained either on the hypothesis of original and 
secondary inclusions or on that of variation in weight of superincumbent strata 
by accumulation or denudation. 
After consolidation the crystal was never crushed, nor was it plastic, nor was 
it permeated by fluids; but during growth it was subjected to rapid alternations of 
salt water and fresh, and to great changes of pressure. 
Dynamic pressure by earth movements, and variation in the weight of superin- 
cumbent rocks, being negatived, there seems to be nothing to fall back upon to 
explain the variations of pressure except irregularly heated water in the vein 
itself. 
Hot salt springs occur in Cornish mines, probably (as shown by the late Mr. 
J. A. Phillips) derived from the sea. 
The phenomena of the Dartmoor veinstones can be explained on the hypothesis 
that sea-water gained access to highly heated granite during the epoch of their 
formation. 
Sufficient heat would vaporise the brine and render possible the inclusion of 
fresh water in the form of compressed steam, in close juxtaposition with an 
inclusion of saturated brine previously entangled by the growing crystal. The 
occurrence of fresh water and brine inclusions close together must be explained 
somehow. 
Any explanation relied on for the veinstones must also cover the case of the 
main mass of the granite, saturated as it seems to have been with salt. 
Under extreme changes of temperature granite cracks throughout without much 
alteration in appearance, but a minutely cracked granite would suck in salt water 
like a sponge either under pressure or by capillary attraction. 
From some cause or other the granite of Dartmoor has been cracked throughout, 
as evidenced by many of the porphyritic felspars. A rise of the isogeotherms, or 
plutonic action, of which latter there is abundant evidence in the elvans and granitic 
veins, are possible sources of the required heat. 
The theory of the marine origin of the saline inclusions in the Dartmoor rocks 
seems to harmonise well with the view commonly entertained that the chlorine 
and chloride of sodium emitted by volcanoes are derived from the sea.' 
In the case of volcanoes the presence of hydrogen and chlorine may be 
1 See Characteristics of Volcanoes, J. D. Dana, p. 8. 
