252 



Besides the determination of the mud held in suspension, that of the 

 coarser particles, the sand and gravel, may reasonably be the subject of inquiry 

 — "a velocity of three inches per second at the bottom of a river is ascertained 

 to be sufHoieut to tear up fine clay, six inches per second fine sand, twelve 

 inches per second fine gravel, and three feet per second stones of the size of an 

 egg." If this be so, some clue might be obtained to this interesting problem 

 by determining the proportion and relative size of the components of the bed of 

 the stream, and the rate at which it moves in different conditions of the 

 flood. It might also be of use to collect water at different depths, especially 

 at the commencement of a flood. But it is evident that this investigation 

 involves questions of great complexity and difliculty, while that of the quantity 

 of mud in suspension is comparatively simple. 



There are some very curious and interesting computations in Sir C. 

 Lyell's Principles of Geology on the quantity of mud carried down by the 

 Ganges. From experiments made by the Kev. Jlr. Everest at Ghazepoor it was 

 computed that during the 122 days of the rain season from June to September 

 the average quantity of solid matter suspended in the water was by weight 

 l-42Sth part, or l-856th part in bulk, giving a total of 6,082,041,600 cubic feet 

 of solid matter in that time. 



"This quantity of mud would in one year raise the surface of 228^ 

 square miles, or a square space each side of which would measure 15 miles, 

 one foot. Now, about I25 cubic feet of granite weigh one ton, and it is com- 

 puted that the great Pyramid of Egypt, if it were a mass of solid granite, 

 would weigh about 600,000 tons. The mass of matter, therefore, carried 

 annually down would, according to this estimate, more than equal in weight 

 and bulk 42 of the great Pyramids of Egypt, and that borne down in the four 

 months of the rains would equal about 40 Pyramids." "The base of the 

 great Pyramid of Egypt covers eleven acres, and its height is about 500 feet. 

 It is scarcely possible to present any picture to the mind which will convey 

 an adequate conception of the mighty scale of this operation so tranquilly and 

 almost insensibly carried on by the Ganges as it glides through its alluvial 

 plain even at a distance of 500 miles from the sea." And even at the point 

 where these observations and calculations were made the Ganges has not been 

 joined by its most important feeders. These drain upon the whole 750 miles 

 of the Himalaya, and no more than 150 miles of that mountain chain have 

 sent their contributions to the main trunk at Ghazepoor ; taking all which 

 into consideration it is probable that the q\aantity of water actually carried 

 down to the sea may be four or five times as much as that which passes 

 Ghazepoor. 



A very interesting discussion followed the reading of Mr. Latouche's 

 paper. It was commenced by the Rev. W. S. Stmonds, who said that he hap- 

 pened to be in London in company with Sir Charles Lyell and Mr. Darwin, 

 when the former referred to a letter he had received from Mr. Latouche on 



