Movement of Scree-Material. 2o7 



An Appendix by Prof. T. G. Bonney, D.Sc, LL.D., F.R.S., F.G.S., 



gave an account of the microscopic characters of the schists, the 

 flattened garnets, the porphyrites, etc., and in this it was pointed out 

 that one set of rocks belonged to an ancient series which, even if 

 wholly or in part of igneous origin, assumed their present mineral 

 structure and condition at an epoch remote from the present, 

 whilst another set was certainly igneous and of more recent date. 



4. « On the Durham Salt-district." By E. Wilson, Esq., F.G.S. 



In this paper the author described the new salt-field in the 

 North of England, occupying the low-lying country bordering the 

 estuary of the Tecs, and situated partly in Yorkshire and partly in 

 Durham. 



The history of tho rise and progress of the salt-industry in South 

 Durham was given, since the first discovery of salt by Messrs. 

 Bolckow Yaughan and Co. at Middlesboro', in the year 1859. 



The stratigraphical position of the saliferous rocks of the Durham 

 salt-district was considered in some detail. The diverse views which 

 have been previously expressed on this head were referred to, and 

 reasons given for concluding that all the beds of rock-salt which 

 have been hitherto proved in this field, and the red rocks with which 

 they are associated, belong to the upper portion of the Trias, viz. 

 to the Upper Keuper series (Waterstones subdivision). 



The probable area of this salt-field, the limits of the distribution 

 and var) ing depths of the chief bed of rock-salt were indicated, and 

 the extent of its supplies pointed out. 



In conclusion, the author called attention to the waste, as well as 

 to certain other disadvantages resulting from the process of winning 

 the salt now in operation. 



5 " On the Occurrence of Calcisphaircc, Williamson, in the 

 Carboniferous Limestone of Gloucestershire." By E. Wethered, Esq, 

 F.G.S., F.C.S. 



6. " Second Xote on the Movement of Scree-Material." By 

 C. Davison, Esq., M.A. 



After briefly recapitulating the substance of his previous paper, 

 the author now communicated the results of experiments continued 

 for a year. He gave a figure in which a continuous line represented, 

 in millimetres, the movements of the upper stone from week to week, 

 whilst a contiguous dotted line indicated the mean ranges of tempe- 

 rature. The rate of descent does not depend solely on the mean 

 range. He gave the following comparison of rates of descent : — 



Average daily 



Total mean 



Eate of des- 



range of 



descent in 



cent in inches 



temperature. 



millim. 



per day. 



14 '4 F. 



8 



•00171 



8°-0 



H 



•00121 



Summer, 184 davs. 

 Winter, 182 days . 



Thus the changes are not altogether proportional to the ranges of 

 temperature, being relatively higher in the winter months. In 



