Mr. Ramsay on the Precipitation of Clay suspended in Water. 329 



The author referring to the fact that clay when suspended in 

 water in excessively minute particles, settles more rapidly when the 

 water contains salts in solution, noticed the opinions expressed by 

 previous writers on the subject, and gave the results of experiments 

 made by him, from which it would appear that the rapidity of pre- 

 cipitation is proportionate to the amount of heat absorbed by the 

 salts in process of solution. By another series of experiments 

 he found that the fluidity of the respective solutions had apparently 

 no influence on the rapidity of deposition of the clay. He also 

 found that clay is deposited less quickly in acid solutions than in 

 solutions of salts, and more rapidly in a solution of caustic soda 

 than in one of caustic potash. In solutions of common salt of 

 different strengths he found that clay settled in the inverse order of 

 their specific gravities. From all these results the author is in- 

 clined to attribute the varying rapidity of the settling of clay sus- 

 pended in saline solutions to the varying absorption of heat by the 

 solutions. When water containing suspended clay was heated, the 

 rapidity of the settling of the clay was proportionate to the heat of 

 the water. The author suggests that the increased rapidity of set- 

 tlement may be due to the greater amplitude of vibration of the 

 molecules of water when heated ; the vibrations being performed in 

 equal times, particles descending at right angles to the plane of 

 vibration will experience less resistance from the molecules of water. 



A note by Prof. Ramsay, briefly indicating some of the geological 

 bearings of these results, was appended to the paper. 



2. " On some Fossiliferous Cambrian Shales near Carnarvon." 

 By J. E. Marr, Esq., 



The shales described by the author extend from about three miles 

 S.W. of Carnarvon to Bangor, running nearly parallel to the Menai 

 Straits. They are faulted against Lower Cambrian to the east, and 

 disappear against a dyke on the west. The shales vary from greyish 

 black to bluish black in colour, and are generally sandy and mica- 

 ceous, but in places chiefly clayey. Fossils were obtained from 

 three places on the banks of the Seiont — namely, near Point Seiont 

 (where the beds are concretionary in structure), along the old tram- 

 way from Carnarvon to Wanttle, and near Peblig Bridge. The first- 

 named locality is richest in fossils ; and here there is a greenstone 

 dyke, parallel to the bedding of the rock, and altering the shales for 

 a distance of about four yards from the edge of the dyke. The 

 fossils seem to indicate that the deposit belongs to the upper part of 

 the Arenig group. 



3. " On the occurrence of the Rhsetic Beds near Leicester." By 

 W. J. Harrison, Esq., F.G.S., Curator of the Town Museum, Leicester. 



The sections described by the author are shown in brick-pits in 

 the Spinney Hills, forming the eastern boundary of the town of 

 Leicester, and in the Crown Hill on the eastern side of a valley 

 excavated by the Willow Brook. In the latter locality they are 

 capped by Lower Lias. They have a slight dip to the south-east. 

 The brick-pits show a thickness of about 30 feet of Rhsetic beds 



