Thirty-second Meeting of the British Association. 439 



osity, and to the disappearance of cholera with the setting in of the 



aurora, the author thinks, may yet be proved to be a display of luminosity. 

 C. Geology. — President, J. B. Jukes. — The President inquired ho'w 

 the variations of the surface called mountains, hills, clifts, g-lens, valleys 

 and plains were formed. He took, first, the formation of great plains, 

 and showed that althoutrh some were formed as plains on horizontal beds, 

 few even of these retained the original surface of deposition, but had 

 more or less a denuded surface. Many equally level plains were low and 

 level, because mountainous masses of rock, often greatly disturbed and 

 contorted, had been removed from above the present surface. The central 

 plain of Ireland, and other plains in the British Islands, were formed in 

 this way. All mountains, except volcanoes or "hills of ejection," were 

 either " hills of circumdenudation," formed by the wearing down and 

 removal of the rocks formerly around them, or "bills of uptilting." In 

 the latter, the lowest rocks appeared in the central parts of the chain, 

 often reared into the highest peaks ; and these central beds dip on either 

 hand under higher and higher groups, which come in as we recede from 

 the axis of the chain. The beds have been raised by mechanical force 

 acting from below; but this, however it had tilted or bent them, could 



sion of moving water. These "hills of uptilting," then, were hills not 

 in consequence, but in spite of denudation, and would have been many 



his belief that all the striking external features were the result of the 

 direct action of the external forces called the "weather," and were not 

 caused by any direct action of the internal forces, which could only reach 

 the surface through the thickness of the crust. He then examined these 

 forces of erosion ; and while he attributed to marine action all the greater 

 and more general features, the great plains, the long escarpments, and 

 the general outline of the mountains, he believed that the valleys which 

 traversed the plains, the gullies that furrowed the sides of the hills, 

 and the glens and ravines on the flanks of the mountains, were all due 

 to the action of the ice or water which fell on them from the atmosphere. 

 He did not give these views as altogether original, but mentioned Mr. 

 Charpentier and Mr. Dana as having long ago applied them to the Pyre- 

 nees and to the Blue Mountains of New South Wales; but, having been 

 long sceptical as to their reality, he now wished to record his conviction of 

 their truth. Mr. Prestwich, Prof. Ramsay and himself, while pursuing 

 different lines of investigation, had all been simultaneously compelled to 

 appeal to the sub-aerial action as the only method of explaining the phe- 

 nomena they had met with ; and Dr. Tyndal had since fallen mto the 

 same line of march. 



On. the last eruption of Vesuvius ; bv l>r. Dauben-y.— The author 

 confines himself to those phenomena which appeared to present some 

 novelty, and to have a bearing upon the general theory of volcanic action. 



phase of action. Its eruptions are more frequent but less violent than 

 they were formerly ; they proceed from a lower level than they did at an 

 earlier period; and they give vent to certaia new volatile or gaseous 



