which I found here is likewise so soft that it may be wrought into a paste with the lingers, but it acquires in a few days a hardness equal to that of fir wood. I have observed the same fact in the disthene which I collected at Boharm in Bamiffshire. It is worthy of remark that the reapplication of water does not restore these minerals to their flexible state. We have yet to learn the chemical explanation of this circumstance.
There is no novelty in the fact I have here brought forward, but sufficient attention has not perhaps been paid in geological writings, to this differing condition of many strata as they exist in the earth, and after they have undergone that change to more perfect induration which they acquire after being removed from their native places and exposed to the air. With regard to many rocks used for economical purposes it is notorious even to workmen. It is easy to see how this circumstance affects many of the reasonings which have been brought forward on the consolidation of strata; a condition of which we see perpetual examples before us, without any ground for supposing that the agency of heat was conducive to that end, and in circumstances indeed where no agency of heat can he imagined capable of producing the complicated effects which have resulted. We are too little acquainted with the chemical laws which regulate the affinity of earths in a state of extreme division, to decide on results which may or may not be produced from either solution or suspension in water. One solitary fact well known in the potteries showing the strong affinity which exists among earths in such a state of extreme division and suspended in water, is sufficient to suggest to its the possibility of affinities still more intense existing among earths in similar circumstances, when their proportions perhaps are different, or where, in addition
