68 REPORT—1848. 
the supposed admission of air and water to the lower regions of the volcanic mass 
through fissures conducting the sea-water to the fluid lava; for supposing such fis- 
sures to exist, it would seem that the fluid matter below ought to ascend into them 
and fill ther, provided the hydrostatic pressure at the bottom of each fissure was 
greater than the weight of the descending column of water, which must often happen, 
especially in such volcanos as Stromboli, in which the permanent position of the sur- 
face of the fluid mass is known to be at a great height above the level of the ocean. 
In reply to this Dr. Daubeny remarks, that M. Gay-Lussac does not deny that 
water gains access to the focus of volcanos, but, on the contrary, asserts that the ad- 
mission of water cannot be doubted, since no great eruption ever occurs that is not 
followed by the evolution of an enormous quantity of aqueous vapour, which, with that 
of the muriatic acid accompanying it, cannot be conceived to take place without an 
admission of sea-water to the interior of the voleano. The French philosopher, in- 
deed, urged the difficulty alluded to only as militating against the notion of the inte- 
rior of the earth being in an incandescent condition, and gives it as a reason for pre- 
ferring the very theory which Mr. Hopkins impugns. The difficulty started, therefore, 
although it may call for explanation from mechanicians, cannot oblige us to reject the 
fact itself, established, as it is, on undeniable evidence; and all that chemists are 
concerned in is to speculate upon the consequences that might result from the admis- 
sion of water to the interior of the earth, as Dr. Daubeny has attempted to do in his 
lately-published Work. : 
Nevertheless, it may be suggested, that the immense pressure exerted by a deep 
incumbent ocean, coupled with the resistance of a considerable thickness of solid rock 
intervening between its bottom and the focus of the voleanic operations, might oppose 
an obstacle to the ascent of lava sufficient to occasion lateral fissures, through which 
the melted matter would find an easier vent at some point on the contiguous land. 
It is true, that fissures of some sort must be supposed to have existed in the rock 
which the sea-water percolates, but these may readily be supposed to have been 
stopped up, at the commencement of each volcanic crisis, by injections of lava, which 
latter cooling in its progress upwards, would create an impediment to the further 
egress of melted matter by the same channels. 
It may be observed, that volcanos do not occur in the vicinity of shallow seas, such 
as the German Ocean, and that many parts of the Mediterranean, near which active 
vents are found, are of great depth. ‘ 
Nor is it necessary to suppose the elastic force equal to what would be required for 
elevating a column of lava to the summit of Etna or Teneriffe, but only such as 
might be adequate to produce the modern eruptions, which always take place from the 
flanks of these mountains; and this degree of elasticity, it is conceived, might be re- 
pressed by the weight of a deep sea, coupled with that of a considerable thickness of in- 
tervening rock, and thereby might determine the issue of the lava at some distant part. 
The recurrence of eruptions Dr, Daubeny has always referred to the cracks occa- 
sioned by cooling in the incumbent rock, whereby a fresh ingress of water to the vol- 
canic focus might be allowed. Be that however as it may, the fact of the presence of 
water stands unaffected by the truth or error of these attempts to account for the 
mode of its introduction. 
Notice of Discoveries among the British Cystidez, made since the last Meeting. 
By Prof. E. Forses, /.R.S. 
At Oxford Prof, Forbes had given an account of this group of fossils, considered 
by Baron von Buch as the lowest Radiate animals and representing the rudimentary 
forms of the superior orders, but believed by the author to be higher than the Cri- 
noids, and leading up from them to the Starfishes and Sea-urchins, Since last year, a 
specimen formerly discovered by Dr. Bigsby in North America, and figured in the 
Zoological Journal, but mislaid, had been re-found, and proved to be a remarkable 
member of this tribe, having a globular body like a sea-urchin, with five depressions 
radiating from the oral aperture, in which arms were lodged; in the space between 
two of the arms was a circle of six ovarian plates. Another specimen very like this, 
but specifically distinct, had been discovered by the geological surveyors in the oldest 
Silurian rocks of Wales, showing that species provided with better arms than any 
other Cystideans appeared as early as the armless species. Some other species had 
