VI 11. A Geological Description of Glen Tilt* 



By John Mac Culloch, M.D. F.L.S. President of the Geological Society, 

 Chemist to the Ordnance, and Lecturer on Chemistry at the Royal 

 Military Academy at Woolwich. 



Read Dec. 3, 1813, and the Supplementary Additions Dec. 16, 1815. 



JLT is well known that the appearance of the granite in various 

 parts of the valley of the Tilt afforded to Dr. Hutton one of the 

 original arguments on which his theory was founded. Hence 

 this spot has acquired among geologists a sort of classical celebrity, 

 sufficient to render it an object of interest, independently of that 

 which is excited by the intricate and remarkable disposition 'of its 

 rocks. Observations, now more numerous than in his day, have 

 brought to light so many facts similar to those which appeared to 

 him so important, that there is no difficulty in pointing out abun- 

 dant instances of an occurrence once supposed rare. But having 

 had occasion while examining these rocks to observe other interest- 

 ing appearances, which have been either misapprehended or over- 

 looked, I consider that a notice of them will not be unacceptable 

 to the Society. The notice is accompanied by such specimens and 

 drawings as are requisite for the illustration of the subject. 



In describing Glen Tilt I have been under the necessity of differ- 

 ing on certain points from those who have preceded me. An ex- 

 amination of many of these points of difference would lead to 

 discussions as endless as they would be fiuitiess, and give this 



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