suspension to rivers flowing directly into the sea.* If this area be annually reduced in level at the same rate as the district through which the Mississippi flows, then the mean level of the land on the globe would be reduced 3 feet in 54,000 years, and consequently the level of the ocean raised 1 foot in the same period by means of the detritus suspended in river-water poured into the ocean.†

But in addition to the sediment carried down by means of rivers, we have also to take into consideration the amount of debris washed into the sea from cliffs during so long a period as that mentioned. It is difficult, however, to form any estimate of what this would annually amount to, for old maps and charts are hardly accurate enough to represent the waste of cliff's by breakeraction even within the last 100 years. Capt. Washington has, however, published a report which gives an account of the encroachment of the sea at intervals on one part of the Suffolk coast. This will give a general idea of the contribution of detritus that may be obtained from some points of a coast-line. The following statements are collected from Capt. Washington's Report on Harwich Harbor in 1844, from which also the figures 4, 5, 6, 7, are copied.

The cliff on the western side of the harbor is about 1 mile long and 40 feet high, and the encroachment of the sea appears to have been at the rate of 1 foot per annum between the years 1709 and 1756, so that the annual supply of detritus was equal to 40 cubic feet for each foot of frontage. Between 1756 and 1804 the advance increased to nearly 2 feet per annum; so that the annual removal of cliff amounted to nearly 80 cubic feet for each foot of frontage.

Between 1804 and 1844 the encroachment of the sea averaged 10 feet per annum, and the annual removal of detritus must have amounted to 400 cubic feet for each foot of froutage. It was during this latter period that extensive dredging for cement stone took place at the base of the cliff.

On the eastern side of the harbor events of an opposite character have occurred, for Landguard Point has gained 50 feet per annum in length during the last 30 years. The addition thus made to the land, and to the "littoral zone," presents an interesting example of the rapid accumulation of a local deposit under favorable circumstances. From the appearance of the beach, it would appear that the shingle and sand of which it is formed

* The proportion of land without rain is about dth of the whole. Keith and Johnston say that nearly one-half the drainage-water of Europe and Asia falls into the Black and Caspian Seas. The proportion for Africa and America is not known.

+ It is not improbable that the solvent powers of rain and river-water are as important agents in the removal of land as the agency above mentioned. Definite calculations on this subject remain to be made.

Tidal Harbors' Commission, First Report of 1845.

Fig. 5--Section showing the Destruction of Beacon Cliff between 1752, 1804, and 1844.

Cliff-foot Rock.

a. Beacon Cliff, with dotted lines indicating the changes that have taken place in high and low-water mark. The dotted line shows the former outline of Languard Point.

have been brought from the north, in which direction there are recorded instances of great destruction of land by storms during the last 300 years. The aspect, however, of much of the coastline appears as if it had remained unaltered for a very long period, except in the manner Mr. R. A. C. Austen* alludes to when he remarks, "that although the sea for months together, and in places even for whole years, may not acquire any fresh spoil, yet there are few hours when its waters are unemployed in fashioning and abraiding the materials already acquired." In considering the effect upon the sea-level caused by sand, mud, and pebbles washed in by the breakers, it is only necessary to regard those materials that may be brought in from cliffs above high-water mark; for the movement of sand and mud below high-water mark can produce no effect upon the sea-level, because the abstraction of these materials from one part of the shore is exactly balanced by their addition to some other part. For instance, some of the flint-pebbles which have contributed to the recent deposit at Landguard Point have been brought along shore a great distance from their original position on the cliff. These flints formed an addition to the sea-bed, and tended to raise its general level by displacing an amount of water equal to their bulk the moment they fell on the shore below high-water mark; and it is quite clear their subsequent movements, either beneath the wave or on the beach, could produce no further effect upon the sealevel, the spaces they occupied on one part of the coast being balanced by the vacancy left at some other. It is also evident that the beach at Languard Point will go on extending so long as the fresh supplies of shingle and sand from the north exceed the removals southward.

Figs. 6, 7.-Sections showing the Increase of Landguard Point between 1804 and 1844

Beach end in 1804.

Beach end in 1844.

a. a. Low-water level of ordinary springs.

In the same manner the continued supplies of pebbles from the westward enables the Chesil Bank to preserve its position. As * Austen, Quart. Jour. Geol. Soc. vol. vi. p. 71-73; and De la Beche, Geol. Observer, 1851, p. 65.

soon, however, as any disturbing causes interrupt the supplies of new material, the sand and shingle beaches dependent upon them must soon disappear; and in fact the termination of every beach will be at that point where the waste and abrasion by breakeraction are balanced by the supply of pebbles and sand drifted from other places. Although it appears clear that only the detritus obtained from cliffs above high-water mark need be taken into calculation, yet I regret to find that scarcely any data of this kind exist, and therefore it is not possible to ascertain the probable effect upon the sea-level that is being produced by the detritus so derived. In the same manner the per-centage of soluble salts in the water of the few large rivers of which notes have been published has not been given separately from the per-centage of matter in suspension, and therefore we are in ignorance of the supplies that are annually introduced into the ocean from the formation of submarine deposits from materials dissolved in the seawater. When the rise in the sea-level from the effect of alluvium brought in suspension by rivers was being considered, I supposed that that cause alone might produce an elevation of one foot in 54,000 years; but in order to make some allowance for the similar effects that must be produced by the introduction into the ocean of materials from above high-water mark on coast-lines* by breaker-action, and also by the formation of submarine deposits from materials which were brought into the ocean in solution, I now propose to consider that all these causes together might produce an elevation of the sea-level equal to one foot in 40,000 years, or three inches in 10,000 years.

Mr. Darwin has remarked, that "the knowledge of any result, which, with sufficient time allowed, can be produced by causes, though appearing infinitely improbable, is valuable to the geologist, for he by his creed deals with centuries and thousands of years as others do with minutes." For these reasons, even if, upon further investigation, it should be found that the true rise in the sea-level is much less than three inches in 10,000 years (in periods undisturbed by subsidences and elevation), yet it may still be an important element in accounting for those changes which we are now about to consider.

(To be continued.)

* The rough estimation of the extent of coast-line, kindly supplied by Mr. A. K. Johnston, (Nov. 1852), is as follows:

ART. IV. On the Phosphate of Iron and Manganese from Norwich, Mass; by Dr. J. W. MALLET.

THIS mineral, first observed by Dr. E. Hitchcock, Jr., and Mr. Hartwell, and since described by Professor Dana and analyzed by Mr. Craw,* possesses much interest from the distinctness of its crystals (which yet in their angles present unaccountable irregularity), since it belongs to a class of minerals which are in general found massive, or but imperfectly crystallized. The following are the results of a chemical examination of some pure specimens, for which I am indebted to Mr. C. Hitchcock. They do not add much to our knowledge of the mineral, but serve to confirm essentially the former determinations by Mr. Craw.

The crystals are opaque and of a dark brownish black color, and give a beautiful violet streak. Sp. gr. 3364, higher therefore than that of the specimen analyzed by Mr. Craw, which he gives as 2.876. Hardness about 5. Before the blowpipe the reactions of phosphoric acid, iron, and manganese, are easily obtained.

A portion of the mineral was pulverized, weighed, and kept for some time at the temperature 100° C. The loss of weight was scarcely appreciable. This portion was then exposed to a bright red heat, and on cooling was found to have assumed a light brownish yellow color, and to have lost 6.33 p. c. In another experiment the loss was 5.97 p. c. To ascertain the amount of water contained in the mineral, a portion, dried as before at 100° C., was heated in a glass tube in a stream of dried air, and the water expelled was absorbed by chlorid of calcium and weighed. It amounted to 1.92 p. c. In another experiment the pulverized mineral was heated in dry hydrogen, and lost 2.18 p. c. of water beyond that formed by the reduction of the peroxyds of iron and manganese to protoxyds.

The phosphoric acid and peroxyds were determined by fusion with carbonate of soda, and the lime, magnesia, and lithia, were estimated in a separate portion. The results of analysis were

*Amer. Jour. of Science, [2] xi, 99, 100.

SECOND SERIES, Vol. XVIII, No. 52.-July, 1854.