390 SECTIONAL TRANSACTIONS.— A. 



Tuesday, August 23. 



Symposium on Seismology (lo.o). 



Dr. F. J. W. Whipple. — Report of the Seismological Committee. 



Mr. J. S. Hughes and Miss E. F. Bellamy. — The International 

 Seismological Summary (10.20). 



Prof. O. T. Jones, F.R.S. — Introduction to discussion (10.40). 



The purpose of the remarks is to emphasise the importance of seismo- 

 logical studies in their application to purely geological problems. Two 

 such problems are of particular interest to Cambridge geologists, the depth 

 of the Palaeozoic floor and the course and depth of certain deep-buried 

 channels, in particular that which runs through Chesterford and Newport, 

 and has not hitherto been traced further. The Palasozoic floor is known 

 directly only in borings, the nearest of which was about thirty miles from 

 Cambridge. Dr. Bullard took up the determination of its depth by seismic 

 methods, and an account of the results will be given by Mr. Gaskell. It 

 is suggested that explosions made in quarrying may be utilised for similar 

 purposes in many parts of the country. 



The investigation of the elastic properties of rocks is also of interest 

 both to seismologists and geologists. The author suggested to Dr. Phillips 

 the study of those of Coal Measure strata, and in the course of some brilliant 

 work he obtained much more definite information about elastic after- 

 working than had previously been obtained. The results may have an 

 important bearing on the operation of stresses responsible for earthquakes 

 and their aftershocks. If this is so it gives another illustration of the 

 advantage of mutual co-operation between geologists and seismologists. 



Miss I. Lehmann. — Characteristic seismograms at different distances 

 (11.20). 



Dr. D. W. Phillips. — Imperfections of elasticity in rocks (11.40). 



A study of the properties of Coal Measure rocks when subjected to different 

 kinds of forces revealed considerable departure from truly elastic behaviour. 

 Very many examples of sandstones, siltstones, mudstones, shales and coals 

 have been subjected to examination in compression, bending and torsion. 



Both the longitudinal and lateral deformations were measured simul- 

 taneously on cylinders of these rocks when subjected to compression. 

 For the first two or three cycles of loading and unloading there was a 

 progressively decreasing set, then for each succeeding cycle there was complete 

 recovery of strain though the stress-strain curve always exhibited ' hyster- 

 esis loop.' There was a pronounced increase in both the longitudinal and 

 lateral deformations when the load was maintained constant. At low loads 

 the lateral time strain was small in comparison with the longitudinal time 

 strain, but as the load increased the lateral time strain became equal to, and 

 sometimes exceeded, the longitudinal time strain. Similar time effects 

 were observed during unloading ; the strains removed immediately on the 

 reduction of load were followed by a further gradual recovery. The elastic 

 modulus and Poisson's ratio usually increased with increase in the load 

 applied. 



When subjected to bending these rocks required, as in compression, two 



