1 68 Geological Society : — Mr. Martin on the Connexion 



lour, I take it out, and pass it for about two seconds over the open- 

 ing of a bottle containing chloride of iodine ; and immediately I put 

 it again in the iodine box, where it acquires very soon the yellow 

 colour, which shows that the plate is ready to be placed into the 

 camera obscura. I have substituted to the chloride of iodine, 

 chloride of bromine, and have found nearly the same result ; but I 

 prefer chloride of iodine as producing a better effect ; and besides, 

 on account of the noxious smell of bromine. 



" The result of my preparation is such, that I have operated in ten 

 seconds with the same apparatus, which, without any chlorine, re- 

 quired four or five minutes ; when using only the original prepara- 

 tion of Daguerre, I have obtained an image of clouds in four 

 seconds." 



GEOLOGICAL SOCIETY. 



[Continued from vol. xviii. p. 590.] 



Dec. 16, 1840. — A paper " On the Relative Connection of the 

 Eastern and Western Chalk Denudations," by P. J. Martin, Esq., 

 F.G.S., was read. 



The author advances this as the first of a series of papers on the 

 construction of that part of the country usually considered as 

 appertaining to the great chalk denudation of the Weald, or more 

 properly, the upburst of the secondary formations between the 

 tertiary of the respective basins of London and Hampshire. 



In venturing on this field of inquiry, he professes also to take up 

 the subject where it was left by him in two former memoirs, one 

 published in 1 828 under the title of a ' Geological Memoir of Western 

 Sussex, with some Observations on Chalk Basins and the Weald 

 Denudation*,' the other in the ' Philosophical Magazine ' for Fe- 

 bruary 1829f; and to extend the number of demonstrative facts that 

 bear upon the theory of denudation by disruptive violence and con- 

 temporaneous aqueous abrasion, there brought forward as a corollary 

 to Dr. Buckland's theory of ' Valleys of Elevation. 5 



In pursuance of this object, he begins by an examination into the 

 arrangement of the great chalk dome of Hampshire and Wiltshire, — 

 the Patria of the chalk of Pennant and Conybeare ; its anticlinal 

 lines of disturbance or upheaval, and their connections with those 

 of the Weald and the smaller western denudations of Pewsey, War- 

 dour and Warminster. 



He finds that six great anticlinal lines are the main instruments 

 of the upbearing of this abraded chalk ; that the three which 

 characterize the smaller anticlinal western valleys are projected 

 onward, and in a manner decussate three others which emanate 

 from the western extremity of the greater valley of the Weald, the 

 vale of Wolmar Forest, from whence he starts his inquiry ; and that 

 these lines do not inosculate or enter into each other ; approxima- 



* An analysis of this memoir appeared in Phil. Mag., Second Series, vol. 

 iv. p. 38. — Edit. 



f Second Series, vol. v. p. 111. 



