164 Dr. C. Davison— British Earthquakes, 1893-99. 



If the views advocated in this paper be adopted, considerable 

 interest will attach to these rocks. The only igneous rock hitherto- 

 recognized as Tertiary in this country to the south of the Cleveland 

 dyke is a solitary dyke which traverses the red rocks of Staffordshire. 



But these Anglesey dykes are a large and important system, 

 much more important than has been generally supposed. They do 

 not give rise to conspicuous features of any kind, and easily escape 

 notice, so that few of them have been hitherto recorded, except on 

 certain parts of the coast. But within the space comprised in the 

 one-inch sheets 94 and 106 (i.e. east of a line drawn from Pentraeth 

 to near Plas Newydd) I have met with no less than 131. A large 

 group also occurs about Holland Arms itself; and though they are 

 less numerous in the centre of the island, a good many still appear, 

 and of the same general type as those near the Straits ; while 

 Mr. Teall's remark above quoted shows that they also occar in the 

 Holyhead area.' They are most numerous of all in the rocky tract 

 known as Mynydd Llwydiarth (in Sheet 94), where 47 occur within 

 a space of a square mile. But there is good reason to believe that 

 they are as plentiful in the drift-covered areas as elsewhere, for the 

 number of boulders they have furnished to the drift is out of all pro- 

 portion to the known exposures, even allowing for their durability. 

 Without supposing, however, that they are everywhere as numerous 

 as on Mynydd Llwydiarth, it is not improbable that they average 

 as many as ten to the square mile in Sheets 94 and 106, which 

 estimate is as high as that given by Necker for the island of Arran 

 (Geikie, op. cit, p. 124). 



Volcanic activity thus appears to have been exerted in Tertiar}"- 

 times not only in North but in certain pai'ts also of South Britain, 

 and this serves to bring the British phenomena perceptibly nearer 

 to those of the Continent. And if the phonolite of the Wolf Eock 

 be, as would seem most probable, of Tertiary age, yet another 

 link is added to carry us, in Tertiary time, across the tract of 

 quiescence which still separates, though now even more widely 

 than then, the volcanic regions of Northern from those of Central 

 and Southern Europe. 



IV. — On some Minor British Earthquakes of the Years 



1893-1899. 



By Charlbs Davisox, Sc.D., F.G.S. 



[Concluded from the March Number, p. 115.) 



Cornwall Earthqualce : Aug. 27, 1895. 



THIS slight, though not uninteresting, earthquake was of intensity 

 4, and occurred at about 12.30 p.m. I have 20 records from 19 

 places, and negative records from 2 places. 



The earthquake is chiefly' remarkable for its small, but elongated, 

 disturbed area (Fig. 2), which is 6 miles long, nearly 2 miles broad, 



1 Some basic dykes recently described from the north of the island do not appear 

 to belong to the same series. (See C. A. Matley, Abstract Proc. Geol. Soc, 

 Jan. 10, 1900, and discussion.) 



