116 Dr. Berger o« the physical Structure 



It Is difficult to account for these differences in the same rock, but 

 though they certainly do exist, I do not think they are sufficient to 

 constitute distinct species. I conceive that in the nomenclature o 

 rocks especially, we ought strictly to adhere to the principle laid 

 down by Saussure — ^" To determine genera and species from those 

 " individuals in which the characters are most distinct, and to qualify 

 " by the name of transitions, those which are doubtful or indistinct."* 



From Lynher Creek, directing our course northward towards Cal- 

 lington, by Saltash and St. Mellion, the grauwacke continues unin- 

 terrupted, but as the country rises, and we approach Kitt-hill, 

 situated about a mile N. E. of Callington, the quantity of quartz met 

 with on the road in blocks and pebbles becomes very remarkable : 

 this indicates our being near the termination of the grauwacke, and 

 we accordingly find it cropping out to-day on the side of Kitt-hill, at 

 about two-thirds of the ascent. Kitt-hill is the nearest place to the 

 sea from the mouth of the Hamoaze, where granite is found in situ* 

 This little hill, though insulated, must be considered as a depen- 

 dance of the mountains of Dartmoor : it is situated on the southern 

 skirt of the granitic mountain-plain of the low range of Cornwall. 



The sides of Kitt-hill are gently inclined ; that on the east Is the 

 most abrupt. The north and south sides are the most extended, and 

 may be considered as the water-sheds. The upper part of the hill 

 is a true granite, composed of crystals of white felspar, quartz and 

 mica. Mr. Necker found in the neighbourhood of Kitt-hill an 

 adventitious mass of tourmaline of a cylindrical form, and of a 

 brownish-green colour, which the Comte de Bournon, to whom I 

 shewed it, considers a new variety of form. From Callington to 

 Plymouth, by Beer Alston, Beer Ferris, and Tam.erton Folliet, as far 



* Voyages dans les Alpes, §. 1945. 



