SECTIONAL TRANSACTIONS.— B, C. 353 



considered when an estimate of the frost resistance of a specified 

 material is required. 



(b) The conditions which induce crystallisation of salts on or under the 

 surface of a porous body. 



(c) The volume changes which take place during the wetting and drying 

 of building materials. 



SECTION C— GEOLOGY. 



Thursday, September 2. 



Excursion preceding the meeting (August 27-September i). 



A Geological Excursion in the Tewkesbury area was held with the object 

 of studying the Pleistocene Geology of the Lower Severn and Avon 

 Valleys, under the direction of Prof. L. J. Wills and Miss M. E. Tomlinson. 



The River Terraces of the Severn between Holt (north of Worcester) 

 and Arlingham (south of Gloucester) and of the Avon near Evesham were 

 examined and discussed. A visit was also paid to the glacial deposits of 

 the Ridgway, south of Redditch. A day was spent on the Frome Valley 

 gravels under the direction of Mr. C. I. Gardiner, who also gave a demon- 

 stration in Stroud Museum of mammalian remains obtained from these 

 gravels, and of reptilian bones recently obtained from the Oolite near 

 Stow-in-the-Wold, Glos. 



Mrs. E. M. Clifford conducted the party round the Barnwood gravel 

 pits near Gloucester, and entertained the members to tea at her home at 

 Witcombe, where a large and interesting collection of mammalian and 

 archaeological remains which she had obtained from the Barnwood gravels 

 were examined. 



The geology of the Nottingham district. 



Prof. H. H. SWINNERTON (10. o). 



Mr. S. G. Clift. 



Mr. P. E. Kent. 



Discussion on The red rocks (11. 15). 



Dr. R. L. Sherlock.— The origin of the red rocks of the North 

 Midlands. 



Late in Carboniferous time Britain was greatly elevated, but the 

 mountainous country suffered rapid erosion of the soft coal-measures 

 strata. Grey detritus was oxidised in an increasingly drier climate into 

 red beds. The red colour has been thought to be caused by chalybeate 

 waters percolating through green beds, but the geological evidence favours 

 both colours being primary, although red may be altered to green super- 

 ficially. Green strata probably indicate wetter climates breaking the more 

 arid periods, the most notable being the Tea-green Marls closing the Keuper. 



Cheshire was probably a sinking land area throughout the period and 



