TRANSACTIONS OF THE SECTIONS. 71 



Ptolemy is nearly correct. His harbour of Staliocanus becomes 2° 48 ,- 81 W. long, 

 and 48° 38 ' lat., which nearly agree with the position of the present harbour of 

 Portrieux, and are probably approximately correct. And, now observe, his mouth of 

 the river Argenis becomes 2° 0'91 W. long, and 48° o2 'o4 lat., which give a position 

 seventeen miles west of the present west-coast of Normandy, which is curiously corro- 

 borated by two modern writers (each independently of the other) having stated that 

 Mont S. Michel was once ten leagues from the sea, which is the distance from the 

 Mont to the mouth of the river Argenis, nearly. Observe also, the mouth of the 

 river ifetus becomes 2° 22'-2 W. long, and 49° 2 '-21 lat., which fall more than thirty 

 miles west of the present west coast of Normandy, and range very well with lligdon 

 shoal and Great Bank, formerly forests. He believed Jersey was not an island until 

 after Ptolemy's time. There. had been a sinking of about 20 fathoms at the 

 Northern Channel Islands ; and sinkings along the French coast of the Bay of 

 Biscay ; but the Aunis has risen a few feet. 



A large collection of contemporary and personal observations, and of facts from 

 modern, medhnval, and classical history, all point in one and the same direction, 

 namely, to establish the certainty of the changes indicated, and several others. 

 Extracts and abstracts from this collection appear in the ' Artisan ' of April, May, 

 &c, 1866. 



The Insulation of St. Michael's Mount in Cornwall. 

 By W. Pengelly, F.B.S., F.G.S., Sfc. 



St. Michael's Moimt is an island at every high water, and, with rare exceptions, 

 a peninsula at every low water. It is about one third of a mile from the mainland. 

 Its name in the ancient Cornish language — " Caraclouse in Cowse," or the " Hoar 

 llock in the Wood," — is entirely inappropriate at present, and betokens a change in 

 the geography of the district since Cornwall was inhabited by a people speaking a 

 language which survived until a very recent period. 



The Mount is undoubtedly the " Ictis " of Diodorus Siculus, whose description 

 is still so very appropriate as to render it probable that two thousand years have 

 produced very little change. 



The insulation must have been effected, of course, either by the encroachment of 

 the sea or by a subsidence of the district. The former hypothesis requires such an 

 enormous amount of time,* and is so utterly opposed to various geological facts, as 

 to render it eminently probable that, since Cornwall was inhabited by a race 

 speaking the British language, St. Michael's Mount was insulated by a general 

 subsidence of the country. 



A Recent Example of the Formation of Pyrites in a South Staffordshire Coal 

 Pit. By Loviboxd Pekcival. 

 The example, which was interesting as tending to throw some light on the for- 

 mation of pyrites in the coal-measures, and further, as having very recently occurred 

 under definite and known conditions, occurred in a West Bromwich coal pit, which 

 was opened about twenty-five years ago, and after a time was closed on account of the 

 rise of water : it remained closed for seven or eight years, and on resuming work, 

 some slack, which had been left in the pit, was found to be largely permeated by a 

 peculiar formation of pyrites. In this case there had probably been a decomposi- 

 tion of pyrites (previously formed), and again the decomposition of the ferruginous 

 salts in solution, by the presence of carbonaceous matter. The quantity of conglo- 

 merate of slack and pyrites thus produced was very considerable. 



On Glacial Striation. By Professor Phillips, LL.D., F.B.S., F.6.S. 

 On few subjects, amidst some apparent differences, are geologists better agreed 

 than on the general theory of the movement of glaciers on their inclined beds in 

 the Alps, while on their former and permanent effects, as evidenced in the valleys 

 and anions: the lakes of England, the differences of opinion are great. The author 

 believed that these differences ought to be brought to the test of accurate mecha- 

 nical principles, such as the limits of effective pressure to move ice forward on level 



