TRANSACTIONS OF SECTION C. 649- 



in a crystalline base partly of calcium carbonate, and partly of iron carbonate. 

 These grains are oolitic in structure, and are probably the result of the same chemi- 

 cal change by which the calcareous beds of the Inferior Oolite in Lincolnshire have 

 been converted into the iron ores. They occur, it will be noted, in several strata 

 above the main bed, 12 feet in thickness in the above section. 



This bed of iron ore is identical with that described by Blake and Hudleston at 

 Abbotsbury in Dorset, where it occurs between the Kimmeridge clay above and 

 the Corallian rocks below. 



It is also physically identical with the valuable iron ore worked for many years 

 at "VVestbury in Wiltshire, where it is met with at a lower horizon, being there 

 separated from the Corallian limestones by 4 feet of marls and sands. 



This stratum, although probably of purely local origin, is to be looked for in the 

 beds above the Corallian throughout the whole of southern England, from Dorset 

 eastwards. Its discovery at Dover is only second in importance to that of the 

 South-eastern Coal-field. It will have to be taken into account in the future 

 development of the coal-fields in southern England. 



6. On the Cause of Earthqiiakes. By J. Logan Lobley, F.G.S., 

 Professor of Physiography, City of London College. 



Although a connection between the cause of volcanic and of seismic action is- 

 generally assumed, neither has been satisfactorily determined, though both are 

 usually attributed in their inception to a shrinkage of the globe from secular cool- 

 ing. The author took exception to this view, and adduced the great amount of rock- 

 folding since the Cambrian Period, as showing that if this were due to planetary- 

 shrinkage, which rock-folding is assumed to prove, the earth's radial contraction 

 must have been at least 100 miles during post-Cambrian ages, that such a contractiort 

 would require a loss of heat to the extent of 5,000° F., that therefore the globe- 

 would have had at the Cambrian Period a temperature 5,000° F. higher than 

 at present, and that such a temperature was altogether incompatible with terres- 

 trial conditions. Neither, apart from greater terrestrial heat, would meteorological 

 conditions be at all like the present, with a surface 100 miles further from the 

 centre, for an attenuated atmosphere and difl'erent gravities would afl'ect all 

 climatal conditions and all the agencies of nature. 



Both the petrological and the palteontological teachings of the Cambrian rocks 

 are entirely at variance with any such conditions, since they indicate terrestrial 

 inorganic conditions and agencies similar to those of the present epoch. 



It was submitted, therefore, that the assumption of a planetary shrinkage waa 

 opposed to geological facts, and that consequently another cause must be sought 

 for seismic phenomena. 



The author thought the hypothesis he brought before the Section in 1888 ta 

 account for volcanic action ' would meet the difficulty, and expressed the opinion 

 that earthquakes were originated by chemical action arising from favouring 

 physical conditions at separate and isolated dynamic foci, at moderate depths and 

 quite unconnected with any central fused mass. These originating foci, like those- 

 of both volcanic and plutonic action, were in a thin outer rind of the globe of a 

 few miles in thickness, which with all its foldings and plications rested upon a 

 solid foundation, giving the earth its ascertained rigidity, and since the Cam- 

 brian Period there has been no appreciable decrease of the bulk of the globe or of 

 terrestrial heat. 



' ' On the Causes of Volcanic Action,' lieport of the British Association for 1888 

 (Bath Meeting), p. 670. 



