Correspondence — A. R. Hunt. 95 



The curious distribution and present position of the Upper Magnesian 

 Limestones in Durham is noticed, and an explanation offered. 



The Permian succession is shown to be more complete in the 

 southern than in the northern area of the county. 



Various sections in the Upper and Upper Middle Limestones in 

 the Hartlepool area are described, among them the recent sinking for 

 Blackhall Colliery, where all the series were pierced, including the 

 full thickness of the Shell Limestone. 



o o i?-iiE3 s:f o isr ID E isr c El . 



SEA-WATER AND CRITICAL TEMPERATURES. 



Sir, — I have been very much interested in Professor Bonney's 

 contribution to "The People's Books" in his Structure of the Earth. 

 Prom repeated inquiries for such a clear and lucid introduction to 

 geology, I know by experience how much such a work has been 

 wanted. 



It is, of course, a great pleasure to myself to note the stress that 

 Professor Bonney lays on Professor Arrhenius' view of the penetration 

 of the rocks by sea-water, both under pressure and by means of 

 capillary attraction; but, in justice to the fathers of geological 

 science, I should like to point out that Sir Henry de la Beche taught 

 the doctrine of the entrance of sea-water into the earth's crust bv 

 pressure ; that Professor Daubree proved by experiment the power of 

 capillary attraction to overcome the opposing resistance of steam as 

 published in 1879 in his Geologie JExperimentale, ch. iii ; and that 

 Professor Judd, in 1881, endorsed and popularized this doctrine in his 

 Volcanoes, what they are and what they teach, pp. 358, 359, besides 

 pointing out the importance of the critical temperatures of liquids in 

 the same work, p. 63. 



Daubree supposed that granite would ordinarily be very 

 impermeable to water, and suggested the possible access of water 

 through dykes of porous rocks ( " par des injections de roches eruptives," 

 loc. cit., p. 242). I, however, in 1890 showed that " under extreme 

 changes of temperature granite cracks throughout ", and that 

 " a minutely cracked granite would suck in salt water like a sponge, 

 either under pressure or by capillary attraction ".^ The experiment 

 is simple, viz., to heat a piece of granite in an ordinary fire, and to 

 soak it when cool in coloured water. I respectfully submit that the 

 important question of the penetration of rocks by water was, long 

 before 1880, promoted from the rank of a mere 'view', even of so 

 distinguished a chemist as is Professor Arrhenius. 



I have often wondered why the convincing experimental demon- 

 strations of Professor Daubree were so completely ignored in the 

 closing decades of the last century, and venture to suggest the 

 following as a possible explanation. In mid-Victorian times all 

 educated people were expected to know something of the Prench 

 language, but they rarely knew German. About 1870 German 



' Rep. Brit. Assoc. 1890, p. 815. 



