!22 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL. 



[March, 



tlie writer enters as it mere into the mind of liis reader, anticipates 

 his difficulties, and by malting himself acquainted with them is more 

 easily able to remove them. This is the great skill in the art of 

 teaching, as in all persuasive arts, to think not of yourself and your 

 own ideas, but how you can best communicate the subject to those whom 

 you are addressing. The mere inculcation of a fact is nothing, you 

 must make the student apprehend it and comprehend it. In attaining 

 this end, we think Professor Ansted has well succeeded, and he has 

 produced a work, which of all those which have appeared, is best cal- 

 ( ulated to be of service to the learner. We must not, however, be 

 iiiisunderstood, this is no cram book, no creation of paste and scissors, 

 the anything good enough for the public ; but carefully elaborated, 

 every fact duly weighed, the knowledge and experience of the 

 author brought to bear, and the latest researches recorded, even to the 

 current period. 



Professor Owen is an authority in every department of compara- 

 tive anatomy, known for his close and ingenious research, the extent 

 of his discoveries, the originality of his views, and the keenness of his 

 discrimination. Those who heard his masterly paper before the 

 Geological Society on Koch's Missourian, can well appreciate his 

 powers, the skill with which he disarticulated the skeleton, showed 

 its true character, and reconstructed it as the Mastodon. It did cer- 

 tainly appear extraordinary that men of science should not have re- 

 cognised the false articulation, when the posterior extremities were 

 made to join on to the caudal vertthrte ; the turning of the tusks up- 

 wards, and the raising of the skeleton on the fore legs were shown 

 to be characteristics impossible and false. His paper on the Amphi- 

 therium in the work before us is no less admirable. The British 

 Fossil Mammalia are arranged not according to any geological peculi- 

 arities, but according to their natural classification, beginning with 

 the Quadrunians, and we have perused this tirst part with deep in- 

 terest, and strongly recommend it to all who are desirous of making 

 themselves acquainted with this important branch of geology, so ne- 

 cessary for the accurate discrimination of strata, and so valuable in its 

 bearing on the higher branches of the science. 



We can scarcely conclude these remarks better than by extracting 

 the preliminary observations of Professor Ansted on the power of 

 water. 



" It requires but little study to discover that every one of the most 

 common and daily operations of nature is concerned more or less in 

 the formation of stratified rocks. Every shower of rain that falls in a 

 hilly or mountainous district, every brook or river that pursues its 

 course through a greater or less extent of country to the sea, or is 

 swallowed up before reaching the sea in some mightier stream than 

 its own, every lake or pool that receives the waters of a river loaded 

 with the particles of muddy soil over which it has passed, and pours 

 forth at its opposite extremity a transparent stream cleared of im- 

 purities, every wave that dashes against a projecting rock on the 

 sea coast, or washes into a hollow bay, tearing and grinding away the 

 solid clift': — each one of these, together with other not less powerful 

 though less frequently recurring agents, is concerned in the formation 

 of new strata, and in effecting changes in the physical conformation of 

 the globe scarcely less remarkable than those with which the geologist 

 has to deal, and which will hereafter be described. A few instances 

 of the actual extent of the effect thus produced will form a useful 

 and interesting introduction to a description of geological facts analo- 

 gous to them. 



"Of the many constantly recurring phenomena, which, owing to 

 their perfect and undeviating regularity, attract but little notice from 

 the casual observer, there is none perhaps more remarkable than the 

 quantity of solid matter held for a time in mechanical suspension in 

 the water of rivers and brought down to be deposited at the mouth of 

 the stream, or spread over the bed of the ocean. The vast amount of 

 mud thus conveyed by running water is occasionally seen in the ex- 

 tensive deltas, or tracts of swampy land, at the mouths of great rivers, 

 such as the Rhine, the Po, the Nile, the Ganges, &c. ; in each of 

 which cases the river divides into so many channels before reaching 

 the sea, that its actual character and apparent magnitude is completely 

 lost. 



" The origin of these vast deposits of rich alluvial soil must be 

 sought for entirely in mud brought from the high lands or the plains 

 through which the river passes, and held in suspension so long as the 

 water is in rapid motion, but which sinks to the bottom wlien the 

 current is checked. To obtain some notion of the actual quantity of 

 solid matter thus continually brought down from the high land to the 

 sea, an experiment was made some years ago by Mr. Leonard Horner, 

 on the waters of the Rhine, the calculations founded on which possess 

 considerable interest. Mr. Horner found that in the month of August, 

 when the river was unusually low, one cubic foot of water taken fairly 

 from near the middle of the river, near Bonn, supplied rather more 



than 21 grains of solid matter, and that in the month of November, 

 when the water was turbid, about 35 grains of residuum were obtained. 

 Now, taking the average of these two observations, and considering 

 the Rhine at Bonn to be 1,200 feet wide, to have a mean depth of 

 15 feet, and to run with a mean velocity of 22 miles per hour, it 

 appears that nearly 400 tons of solid matter would pass down the 

 stream per hour; and that in the course of one year, between seven 

 and eight thousand millions of tons woidd be carried along, the greater 

 part of which must be deposited in Holland before reaching the sea, 

 in consequence of the slow and meandering course of the river through 

 that flat alluvial country. In the course of 2,000 years, the Rhine may 

 thus have brought down enough material to form a stratum one yard 

 thick, extending over an area more than 3G miles square. 



"But the delta of the Ganges far surpasses in magnitude that of any 

 European river; and is on the whole, perhaps, the most extensive and 

 remarkable of all those at present forming of which we have any accu- 

 rate data. The head of this gigantic delta commences at a distance 

 of 220 miles in a direct line from the sea, and the base of it is 200 

 miles in length ; the whole triangular space occupied comprising up- 

 wards of 20,000 square miles, every part of which has been formed by 

 deposition from the river and its tributaries. 



" The quantity of mud and sand carried by the Ganges into the Bay 

 of Bengal is however, notwithstanding the vast deposit which pre- 

 viously takes place, still so great, that during the rainy season when 

 the stream is turbid, the sea does not recover its transparency even at 

 a distance of GO miles from the coast; and the quantity of mud held 

 in mechanical suspension is so great, that a glass of water taken out 

 of the river when at its height, is said to yield one part in four of 

 mud. Calculating from the dimensions of the river and the rate of 

 the current, Major Rennel has shown that during the flood season the 

 weight of the mud thus brought down daily, and deposited either 

 within the limits of the present delta, or at the mouths of the different 

 branches, must be as much as 450 millions of tons, a quantity which is 

 perhaps more readily understood by expressing it as equal to about 

 74 times the weight of the Great Pyramid of Egypt, supposing that 

 to be a solid mass of granite. 



"Another instance of a vast amount of solid matter conveyed by a 

 river, and spread out upon the bottom of the ocean, is seen in the dis- 

 tribution of the sediment of the great river of the Amazons. At the 

 point where the current formed along the coast of Africa, (a current 

 which crosses the Atlantic to the continent of South America,) meets 

 the stream of the Amazons, it runs at the rate of about four miles per 

 hour. The stream of the river, however, preserves part of its original 

 impulse, and its waters may be recognised by their muddy colour, and 

 are not wholly mingled with those of the ocean at a distance of 300 

 miles from its moulh. An immense tract of swamp is being formed 

 along the coast of Guiana by the deposit of the mud thus brought 

 down by the Amazons, and the shallow sea along that coast is rapidly 

 being converted into land. 



" The power of water when in motion of transporting not only mud, 

 but heavy bodies of considerable magnitude, is another point of con- 

 siderable interest in geology, and one that requires to be stated in 

 some little detail, because there are certain popular fallacies concern- 

 ing the motion of heavy bodies, which tend much to confuse and mis- 

 lead the judgment on this subject. 



" We are accustomed to consider weight as an absolute quality of 

 certain bodies, which we therefore call heavy. Now this quality of 

 weight, as the word is commonly applied, is in fact only relative ; and 

 in this relative sense, a piece of wood is no more heavy when im- 

 mersed in water than a balloon filled with hydrogen gas is in the air, 

 each being lighter or of less weight than an equal quantity of the 

 element in which it is placed, and which it displaces. In all cases, 

 the actual weight of that quantity of the fluiil which would have 

 occupied the space filled by a solid body, must be di-ducted from the 

 actual weight of the body before the relative weight, — the only part 

 which resists motion, — can be calculated. 



"Speaking accurately, therefore, bodies of all kinds are heavier in 

 air than they are in water, and are consequently moved with greater 

 facility in the latter, than in the former fluid. It should also be borne 

 in mind that the power which water possesses, of transporting heavy 

 bodies, increases in an enormous ratio with the increase of rapidity of 

 the current; and with these considerations, we shaU be able to account 

 for, and understand statements on record, otherwise almost incredible, 

 of the effects produced by water in rapid motion. 



" As a recent instance of effects of this kind, and one occurring in 

 our own island, 1 quote an account of an extensive flood, which spread 

 simultaneously over a large tract of country, in Aberdeenshire, in the 

 early part of August, 1S29. The total length of river flooded on this 

 occasion could not be less than between five and six hundred miles, 

 I and the whole of the river courses were marked by the destruction of 

 bridges, roads, crops, and buildings. 



