Geological Society of London. 85 



Discussion. — Mr. Evans thought that the fact of the mud from some of the 

 cones having ceased to flow was in favour of the theory of their being due to 

 hydrostatic action, the outflow ceasing when the pressure .was insufficient to over- 

 come the resistance, and a fresh vent being found elsewhere. 



Mr. Forbes had frequently observed the mud-craters of Peru, which were un- 

 doubtedly due to volcanic action, though in many instances the outflow was cold, 

 or nearly so. In the cases described by the author it was, however, possible that 

 they might be due to another cause. 



Prof. Phillips mentioned a spring which rose through mud in Bridlington 

 Harbour, and from which the outflow was greatest at low water ; but the spring 

 tides in the Persian Gulf might, on the contrary, effect a rise in the mud-craters by 

 obstructing some passage by which mud was discharged into the sea. Were this 

 so, the upward movement in the crater would on each occasion probably occur 

 somewhat later than the high tides. 



Mr. Seeley remarked on the presence of undoubted volcanic action in the district, 

 in the shape of hot springs, &c., and therefore questioned the propriety of bringing 

 in hydrostatic pressure to account for the phenomena. 



Mr. Miller cited the mud-volcanos of Iceland as instances of pure volcanic 

 action, and drew a distinction between the occurrence of mud-craters near the 

 sea and at a distance from it. 



The Author, in reply, observed that he had merely suggested the possibility of 

 the outflow being due to hydrostatic pressure, and did not insist upon it. He 

 stated that there was ample evidence of volcanic action at a distance of 200 or 300 

 miles from the district h-e had described. 



II.- December 17th, 1873.— Prof. Eamsay, F.E.S., Vice-President, 

 in the Chair. The following communications were read : — 



1. " Observations on some Features in the Physical Geology of 

 the Outer Himalayan Eegion of the Upper Punjab, India." By 

 A. B. Wynne, Esq., F.G.S. 



The district of the Upper Punjab described by the author con- 

 sists of crystalline, granitoid, syenitic, and schistose rocks far in 

 among the hills, succeeded by slates and limestones, possibly of 

 Silurian age, unconformably overlain by Triassic and perhaps older 

 rocks, which are in their turn unconformably succeeded by a series 

 of mutually conformable Jurassic, Cretaceous, and Nummulitic Lime- 

 stones, and shaly beds. These Secondary and Tertiary beds, which are 

 chiefly limestones, are called the " Hill Limestones." Beyond these 

 comes a zone of hills and broken plains, composed of sandstones, clays, 

 and conglomerates, of great thickness and of Tertiary age (Eocene 

 and Miocene), which the author calls the *' Murree beds." This belt 

 passes generally along the whole southern foot of the Himalayas, 

 from Assam to Afghanistan. In the district described by the 

 author it is bounded on the south by the Salt Range, beyond which 

 stretch the deserts of the Punjab and Sind. 



The outer Tertiary belt presents a gradation towards the hill 

 character. Among the rocks of the Murree zone there are harder 

 beds than elsewhere ; limestones occasionally appear, sometimes 

 like those of the hill-beds, and the Hill Nummulitic Limestones may 

 have alternated in their upper part with the Murree beds.. The 

 Nummulitic Limestones of the Salt Eange, containing large Bivalves 

 and Gasteropoda, were probably of shallow-water origin, whilst the 

 diminutive organisms of the Hill Nummulitic Limestone inhabited 

 greater depths. 



