ON PHOTOGRAl'IIS i)F GEOLOli ICAl. INTEREST. ;)t)i) 



Hock-Jnaaaex and their delations, 

 Eegd. 



No. 



F. 11 Alternations of Basalt lava and ' Cascade Section,' Mont Dore, Auvergnc, 



tuff. Franco. 40 S. 



2374 Weathered-out Lamprophyre North of Beinn Mhialairidh, near Glenelg, 



dyke. 40 S. 



Characteristic Hocks and Landscapes, 

 Palceozoic. 



2377 Actinolite in Lewisian Gneiss . Half a mile south of Sandaig Burn, near 



Glenelg. 40 S. 



138 Coal-measures above Eeoston Longley's Brickyard, Leeds. 5S P. 



Bed. 



139 Coal-measures including Beeston Grosvenor Brickyard, Leeds. 58 P. 



Bed Coal 



140 Coal-measures above the Crow Boyle's Quarry, Leeds. 58 P. 



Coal. 



141 Coal-measures including Crow „ „ „ 



Coal. 



142 ' Black Bed ' Coal Seam . . Dolly Lane Brickyard, Leeds. 5S P. 



143 ' Better Bed ' Coal Seam . . Benson Street Brickyard, Leeds. 58 P. 



Mesozoic. 

 990 Paramoudras in Chalk . . Soldierstown, Moira, Antrim. 5G I'. 



Names and Addresses of Donors and Plwtographers. 



9. R. Welch, Lonsdale Street, Belfast. 

 15. A. S. Reid, Trinity College, Glenalmond, Perth. 

 21, Professor E. Waymouth Reid, University College, Dundee. 

 40. A. K. Ci>omara-Swamy, Walden, Worplesdon, 'xuildford. 

 49. Miss B. M. Partridge, 75 High Street, Barnstaple. 

 56. W. Gray, Glenburn Park, Belfast. 

 68. F. W. Branson, 14 Commercial Screet, Leeds. 

 59. H. W. Monckton, 10 King's Bench Walk, Temple, E.G. 



On the Geological Age of the Earth. By Professor J. Joly, D.Sc, F.E.S. 



[Ordered by the General Committee to be printed in extenso.'] 



On account of a certain small amount of arithmetical complexity involved 

 in the statement of the method of estimating the age of the earth by 

 solvent denudation, I have had a brief summary of it put into print, all 

 the quantities involved being calculated into the metricid system of units 

 (see Appendix). With this in your hands I may be permitted to leave 

 figures aside in the few remarks I have to make. 



In this method, as the President of the Geological Section has already 

 stated, the sodium contained in the sea is assumed to be a measure of the 

 total amount of solvent denudation since the oceans were formed, and 

 the amount of sodium annually supplied by the rivers is taken as a 

 measure of the rate at which this denudation has been effected. Why 

 attention is restricted to the sodiiom need not be enlarged upon further 

 than to say that every other element supplied by solution of the rocks is 

 again rejected by the sea to an extent which renders it unavailable. 



It will be found on reference to the summary that allowance is made 

 for the efiects of the probable amount of active acid primevally uncom- 

 1000, BO 



