Eoivard Fox— Soda Felspar Rock—Dinas Head, N. Cornwall. 13 



arguments which support the view he defends, and leaving out all 

 the others. 



Still, I think that, after reading Seebohm's graphic account of the 

 extraordinarily sudden triumph of summer, no one will be disposed 

 to adopt Croll's view as set forth in (E). 



(F) It seems hardly necessary to discuss this argument now. It 

 is easy to see, and is shown in the paper already referred to, that 

 there is even less difference, so far as sun-heat is concerned, between 

 our present climate and that of the supposed "genial age" than 

 between our climate and that of the supposed " Glacial age." 



(G) Whether the stoppage of the Gulf Stream would result from 

 a great lowering of temperature over the northern hemisphere is 

 a point I am not prepared to give an opinion upon. But as an 

 argument in connection with the astronomical theory, it is absolutely 

 dependent on the previous acceptance of (C), (D), (E), and (F), and 

 as these have been shown to be quite erroneous, it is unnecessary to 



examine into (G). n r- r\ ^^ 



(H) In taking this position as to the summer fall of snow, broil 

 shows such a courageous resolve to take the bull by thehorns, that 

 a close criticism seems too prosaic, and the best course is to allow 

 (H) to march out with all the honours of war. 



[To he continued.) 



III.— On a Soda Felspar Eock at Dinas Head, North Coast of 



Cornwall.^ 

 By Howard Fox, F.G.S. 



DINAS HEAD is a promontory 4 miles west of Padstow, jutting 

 out into the sea from Trevose Head, and separated from it by 

 an isthmus about 100 feet above sea-level, which is washed clear of 

 soil by the ground seas which sweep over it from the north. The 

 headland is 165 feet above sea-level at its highest point, and is 

 almost as broad from north to south as it is long from east to west. 

 The base and foreshore of the headland appear to be _ entirely 

 composed of greenstone containing much calcite. The microscope 

 shows it to be probably an altered dolerite. 



Between the greenstone and the slate of the district, as well as 

 interbedded with the slate, we find a rock that covers about an 

 acre, and assumes various characters, but all of which contain nearly 

 10 per cent, of soda and from 64:-4 to 66-6 per cent, of silica. The 

 compact varieties of this rock are crypto-crystalline, and may easily 

 be mistaken for cherts. The concretionary and spherulitic varieties 

 show grains and blades of a felspar, which is doubtless albite. _ It 

 varies in colour from creamy-gray to light-brown and dark bluish- 

 gray ; it weathers white, and is often studded with cavities, someof 

 which are not unlike pholas-holes. These cavities are filled with 

 a rusty-brown material containing crystallized quartz. In other 

 places this rock contains lenticles and concretions of calcareous 

 matter of considerable size, and, when it is interbedded with slate, 

 it is densely studded with small rusty-brown spots, sometimes 

 1 Eead at the British Association Meeting, Oxford, August 10th, 1894. 



