248 Dr. Mac Culloch on a 



Dismissing this part of the subject for the present, the 

 artificial results which form the first part of this paper are 

 interesting, even in an abstract chemical view, from their con- 

 nexion with the analogous changes which so many other solid 

 bodies undergo from the action of heat. In any point of view, 

 a fact so solitary and unexpected is deserving of record. 



With respect to the geological facts which form the second 

 division of this paper, they are, indeed, too rare to be very 

 satisfactory, since they seem rather to belong to the class of 

 exceptions than rules. Yet I trust it will appear, that they 

 are united by one common band which removes them from the 

 class of insulated facts, and gives them a more general interest. 

 Increased observations will probably add to the number ; and 

 by tracing various circumstances not to be found in these, by 

 which they may be accompanied, geologists may ultimately 

 establish a principle capable of explaining phenomena which 

 have hitherto been a source of no small difficulty. Should even 

 the phenomena here described prove incapable of being con- 

 nected with any important general principle, their singularity 

 and rarity render them worthy of record. The appearances at 

 Dunbar, in particular, have been so much misunderstood, or 

 so inadequately examined, that it seemed necessary to place 

 them in a clearer point of view. I can only regret the want of 

 materials sufficient to furnish a better connected train of evi- 

 dence, on a subject which appears to comprise important con- 

 sequences in geological science. 



Some phenomena, which take place in glass, and in other 

 solid bodies exposed to a continued heat incapable of bringing 

 them into a fluid state, induced me long ago to undertake a series 

 of experiments on this subject. Some valuable results were ob- 

 tained, which I shall probably take some future opportunity of 

 communicating through the medium of this Journal ; but the 

 impossibility of preserving a continued heat for a sufficient 

 length of time in a common laboratory, ultimately caused these 

 experiments to be abandoned. Among other substances, it 

 was attempted to change the internal arrangement of those 

 rocks, which have been supposed to owe their origin to igneous 

 fusion, by the application of a heat incapable of producing that 

 ultimate effect. But the defects of the furnaces already alluded 



