TKANSACTIONS OF SECTION C. 587 



disturbances. (3) If the effective earth currents are supposed to be deeply seated 

 ■within the earth — possibly in strata of hifjlier conductivity — it becomes more 

 difficult to account for the local character of the magnetic disturbances. (4) The 

 authors' observations prove that the disturbing forces tend towards points and 

 lines, and if earth currents produce them th*>j' must circulate round the districts 

 thus indicated. It is diUlcult to suggest a physical cause wliich would produce 

 such an I'lfcct. (5) On the other hand, the authors found that in several cases the 

 centres or lines of attraction are closely connected with the presence of magnetic 

 rocks, and especially wit li basalt. The Western Isles of Scotland, the coalfield in 

 South Scotland, the north of Ireland, and Mid-Wales and Shropshire all present 

 centres of attraction, and are all marked by the presence of large quantities of 

 basalt. 



In two cases where loci of attraction are not connected with visible igneous 

 rocks they nevertheless occur in places where there is reason to believe that the 

 older rocks approach near to the surface. This is the case in south-east Yorkshire, 

 and along a line which runs from London to South Wales, and possibly to Wexford, 

 which agrees in general direction with the I'alteozoic ridge which connects the 

 coalfields of South Wales and IJelgium. 



On the whole, then, the authors think that the theory of the direct action of 

 magnetic rocks agrees best with the observed facts ; and they show that the king- 

 dom can be divided into a small number of magnetic districts, in which the 

 directions of the disturbing forces are evidently closely connected with their 

 geological constitution. 



The authors have prepared, with the kind help of Professor Judd, F.R.S., a 

 map, which shows the main geological features of the country, and also the main lines 

 toward which the disturbing magnetic forces act. The latter are closely associated 

 with the following geological features: (1) the fault line of the Caledonian Canal; 

 (2) the basalt of the Western Isles of Scotland ; (3) the basalt of the coalfield in 

 the south of Scotland ; (4) the region in south-east Yorkshire in which the Jurassic 

 strata thin out; (5) the basalt in Mid-Wales and Shro]ishire ; (0) the line of the 

 Palaeozoic ridge ; (7) the basalt of Antrim ; (8) the igneous rocks of Connemara. 



All the principal masses of basalt in the kingdom thus form centres of magnetic 

 attraction, and two lines of attraction (in Yorkshire and the south of England) 

 occur in places in which the older rocks are supposed by geologists to approach 

 the surface. In one or two cases, and notably near Kells in Ireland, a well- 

 marked magnetic centre of attraction occurs in a place where no known geological 

 feature serves to account for it. On the whole, however, the connection between 

 visible basaltic masses and loci of magnetic attraction is so marked that it can 

 hardly be doubted that elsewhere magnetic attractions indicate the presence of 

 concealed igneous rocks, and afford a means of approximately tracing their distri- 

 bution relatively to the surface sedimentary deposits by which they are concealed. 



TUESDAY, SEPTEMBEli 17. 

 The following Papers and Reports were read : — 



1. Notes on the Geolo<iy of Torres S fruits. 

 By Professor A. C. Ha'ddon, M.A., M.R.T.A. 



After having examined a number of the islands in Torres Straits, I can fidly 

 confirm the triple division of the islands made by Jukes. The lines of longitude 

 142° 48' K. and 143° 30' E. conveniently demarcate these subdivisions. 



The islands to the west are all composed of old igneous rocks and are surrounded 

 by fringing reefs. The central group is composed of low coral islets formed by 

 wind and wave action. The eastern islands Uga, I'>ub, and the M urray Islands, 

 are of volcanic origin, and are also fringed with coral reefs. There are numerous 

 large and small coral reefs in the Straits, but no atols. 



