70 



wise might have passed unnoticed. It is however a curious 

 circumstance that they have not been discovered elsewhere, 

 although Petroleum, Naphta, and analogous substances, as 

 Maltha, Mineral Tar, Pitch, and Asphaltum, which are 

 nearly related to the above, are found in many parts of the 

 world, as well as at Castleton, where this substance is 

 found. These always differ from the vegetable substances 

 of the same nature (viz.) common Tar and Pitch, by their 

 peculiar odour, which somewhat resembles oil of brick, 

 used by Lapidaries, and which I understand is a kind of 

 burnt oil. It is very different from the well known scent 

 of Pitch and Tar. Vegetable Caout-chou differs from both. 

 So, we may say that the under-ground change seems to be 

 the cause of the odour. We cannot at present account for 

 the elasticity, otherwise than in the words of the ingenious 

 Mr. Hatchett in the Linnean Transactions : " From what 

 I have already related, I suspect that the elastic property is 

 occasioned by the interposition of very minute portions of 

 air, or some other elastic fluid between the parts of the 

 Bitumen, and that this takes place by means of some un- 

 known cause at the time of formation ; for, when these 

 Bitumens are melted, the elastic fluid is liberated, and the 

 mass loses that fine spongy texture which I suspect to have 

 been the cause of the elastic property*" 



It is somewhat curious that it is found as it were oozing 

 out of, or attached to, the rocks. The present specimen 

 is attached to common Limestone rock, mostly Stinkstein: 

 seep. 81 Brit. Min. It is nearly the softest of the elastic 

 sort : 'some parts of it are almost in an oleaginous state, and 

 stick to the fingers. It is nearly the colour of common 

 Caout-chou, but will not stretch out like it, although it 

 springs to its form after compression ; and hence it differs a 

 little from Caout-chou, as the indenture of the impression 

 is not so easily made permanent. It is by no means so 

 tough as common Indian rubber. 



