286 Dr. Mac Culloch on the Geology ofGleti Tilt. 



which I found here is likewise so soft that it may be wrought into 

 a paste with the fingers, 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 BamfTshire. 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 oeconomical purposes it is notorious even to work- 

 men. 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 be imagined capable of producing the complicated 

 effects v;hich 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 suspen<^ion 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 us the possibility of affinities 

 still more intense existing among earths in similar circumstances, 

 when their proportions perhaps are different, or where, in addition 



