136 GEOLOGY OF THE LOTHIANS, 



APPENDIX I. 



SIR JAMES HALL'S EXPERIMENTS. 



When describing the relations of the trap-rocks of the 

 Lothians to the Neptunian strata, we have casually remarked? 

 that it was from an examination of them that Dr Hutton 

 first formed those theoretical opinions concerning their mode 

 of formation, which are now universally adopted by the 

 cultivators of geological science. From Salisbury Crags, 

 Arthur Seat, and numerous other points in the district of 

 the Lothians, that ingenious philosopher and acute observer 

 drew conclusions in regard to the past history of the world 

 which, even on their first proposal, were adopted by many, 

 and zealously defended by not a few. In the present ad- 

 vanced state of geology, it may appear to some that the 

 several phenomena which Dr Hutton first pointed out in 

 regard to the trap-rocks, and the appearances which the in- 

 dividuals of the stratified systems exhibited, when near them, 

 were of so clear a nature, that they could be explained only 

 in one way ; but it must be remembered that the plutonic 

 origin which he awarded to the trap-rocks, and the changed 

 state in which he said certain strata existed, were as yet to 

 be considered as theoretical, and could not be proved by di- 

 rect experiment. Compression under water or solid strata 

 had been stated to be a cause sufficient for the production 

 of a crystalline structure in masses cooling down from an 

 original state of igneous fusion, but the chemist had not as 

 yet demonstrated this by making a homogeneous vitreous 

 mass acquire a granular arrangement. 



