14 
side. The present specimen, however, is remarkable for 
the incurved structure of the Sept. 
Perhaps an attention to the nature of the subject will 
give a theory for the cause, or lead us nearer to the cause 
in question. Thus the general contrarieties of heat and 
cold may be the cause. Clay cracks from contraction in 
cold or frost, giving out much of its water into the fissures, 
which latter, becoming impregnated with Quartz (which 
may be crystallized from a saturated solution in any me- 
dium), thus retains its position, and afterwards the water 
may wash away the Clay under various circumstances. 
I do not know whether it is pure water that forms in the 
cracks of frosty Clay; perhaps it may be impregnated with 
Quartz, whose natural temperature will not allow above 
a certain quantity to remain with the Clay*. This might 
be really of consequence enough to be inquired into by 
those who have the opportunity. 
* Common Clay is mostly a mixture (strictly speaking) of Silex and pure 
Argilla, and is often so called when the Quartz contained in it amounts te 
sixty, or even ninety, per cent. 
