302 
nearly filled with water, as described in my paper in the 
Quarterly Journal of the Geological Society, (Vol. XIV., 
p. 453) and, in accordance with the principles therein 
explained, they indicate that the rock was consolidated 
nnder a very great pressure. These fluid- canities show the 
spontaneous movement of the bubbles which they contain, 
better than those I have seen in any other rock. 
I am to a considerable extent prepared to admit that in the 
experiments made by Mr. Marshall there was some separation 
of the constituents, and that consequently the comparison 
with the natural rock is not everything that could be 
wished. The hornblende melted more easily than the quartz 
and felspar, and a portion of those minerals has risen 
upwards, and thus the whole was not thoroughly incor- 
porated. However, the general character of the product 
obtained by the fusion of a granite of the Vosges, which, 
along with other most interesting specimens of similar sub- 
stances, has been kindly sent to me by M. Delesse, of Paris, 
shows that, even if we must make some allowance for a 
change in composition, the difference between the artificial 
and natural stone is not dependent on that cause alone, but 
that an explanation must be sought for in the very different 
circumstances under which they were formed. 
In some parts of the product obtained on fusing 11 cwts., 
which appear to have cooled more quickly than the rest, very 
curious concretions, composed of radiating crystals of black 
oxide of iron, have been formed, scattered about in the black 
glassy basis, which has been deprived of its iron and 
rendered colourless in their immediate vicinity, so that, when 
seen with the microscope, they present a very curious appear- 
ance, in fact, if such a comparison may be allowed, they look 
very much like annular eclipses of the sun. Some of these 
concretions are larger than the rest, and contain in the centre 
crystals of another substance. In other portions of the same 
