Beviews — Metamor2)/nc Rocks, etc, in Tijrone and Donegal. 573 



nearly to its original level. The shock was also recorded by 

 seismographs at Catania, Portici, Ischia, Rocca di Papa, Eome, Siena, 

 Pavia, and Nicolaiew (1,009 miles from the epicentre) ; and the 

 diagrams given by several of these instruments show two or more 

 groups of oscillations. 



Prof. Eicco has made some attempts to determine the depth of 

 the seismic focus, but the results do little more than illustrate the 

 imperfection of the methods employed. From the recorded times at 

 Catania, Ischia, and Rome, he estimates it at 99 miles ; and from the 

 time-curve corresponding to eight good observations, at 107 miles. 

 Mallet's method was inapplicable, and Button's gave values ranging 

 from 13 to 100 miles. 



Prof. Mercalli's numerous observations on the direction of the 

 shock have an important bearing on the origin of the earthquake. 

 He shows that there are two small areas in which the directions 

 intersect, one on the north-west slope of Montalto d'Aspromonte, 

 between Plati and Delianova ; the other in the sea, a few miles from 

 the coast, between Palmi and Cape Peloro. Recalling the double 

 character of the shock, he concludes that the earthquake originated 

 in two foci, the one beneath the sea being the last in action and 

 giving rise to the strongest part of the shock. C. Davison. 



III. — On Metamorphio Rocks in Eastern Tyrone and Southern 

 Donegal. By G. A. J. Cole. Trans. Roy. Irish Acad., 1900, 

 vol. xxxi, pp. 431-472. 



On certain Rocks styled ' Felstones ' occurring as Dykes 

 in the County of Donegal. By G. A. J. Cole and J. A. 

 Cunningham. Scientific Proc. Roy. Dublin Soc, 1900, vol. ix 

 (N.S.), pp. 314-324. 



THE problems presented for investigation in the complex regions 

 of crystalline rocks near Pomeroy in Tyi-one, and Pettigo in 

 Donegal, are stated, in the first paper, as a series of questions — 



(i) Is the intrusive granite distinct from the gneiss, or is the 

 former merely an ofl'shoot from the latter ? 



(ii) Is the gneiss itself an igneous rock, and if so, has it assumed 

 its local richness in ferromagnesian minerals by absorption of basic 

 and other rocks adjoining it ? 



(iii) If the gneiss is distinct from and older than the granite, 

 what claim has it to be regarded as Archaean and fundamental ? 



The author favours the view that the gneiss has been produced 

 by the intricate intrusion of a granitic magma into ancient schists, 

 which may originally have been of sedimentary origin. The gneisses 

 thus produced, as well as the less altered schists, are travei'sed by 

 and included in the granite of the Slieve Gallion type, which also 

 cuts an overlying basic igneous series, the latter giving rise to 

 ' eyes ' of amphibolite. The paper is illustrated by two plates, one 

 of them coloured. 



