152 Dr. Berger on the physical Structure 



appears in the form of rounded nodules, giving the rock a porphy- 

 ritic appearance. It is very common to find cavities in it, Uned with 

 crystallized tourmaline, I did not see this rock in siiii^ but it is so 

 abundant in this district, that I suspect it forms a subordinate bed 

 in the granite, perhaps as the matrix of an ore : in the vicinity of 

 the Land's-end, the granite is often accompanied w^ith masses of 

 black schorl, both amorphous and crystallized. 



From St. Just, which is four hundred and four feet above the 

 level of the sea, the granite continues as far as the neighbourhood of 

 St- Ives by Botallach, Morvah, and Zennor, though only at a short 

 distance from the sea. It must however be observed, that the height 

 of the granitic plain continues, and even increases as we advance. 

 Thus, the highest point of that part of the road, in the neighbour- 

 hood of Mean Screefis, is six hundred and twenty-three feet above 

 the level of the sea. The tors in that part of the country rise 

 ins uccession, and form an almost uninterrupted boundary to the 

 south of the road. Near St. Ives, the country suddenly lowers, and 

 we enter the grauwacke, but at what place, or at what height, I 

 cannot say. 



Leaving St. Ives for Redruth, the road crosses a hill, the top of 

 wliich lies to the right ; it is granitic, but the common grauwacke 

 having a very fine and close texture, appears on its side. The ter- 

 mination of this rock is pretty near the highest point of the road. 

 Being in a hurry to pass the river Heyl, which can only be forded at 

 low water, I had not time to determine the exact height. 



The mouth of the Heyl lies in a small inclosed bay between St. 

 Ives and Godrevy, situated N.N.E. of Mount's Bay. By these two 

 bays this part of Cornwall is formed into a kind of isthmus. A great 

 deal of sand is heaped up in St. Ives' Bay, particularly on the east side, 

 forming small sand hills between Gwithian and Phillack. 



