adequate; and so the conclusions which have been reached by various investigators concerning the quantity of solid matter annually carried by rivers to the sea are without sufficient basis. We have already observed that an analysis of river water, taken at a single point and at one stage of concentration, tells us little or nothing of what the stream as a whole may do. Annual averages of water taken near the mouths of rivers are needed before the problems of chemical denudation can be even approximately solved.

For example, Sir John Murray," whose figures were cited at the beginning of this chapter, has computed, by averaging the analyses of nineteen rivers, not only the total amount of saline matter carried annually in solution to the sea, but also its composition. His results are as follows, together with a reduction to percentages, stated in terms of ions:

Saline matter carried annually to the sea by nineteen rivers.

This estimate, combined with the figures previously given, is interesting, for it shows the magnitude of the quantities involved in the discussion and emphasizes the preponderance of carbonates in river water. But it can not be applied in anything like an exact way to determining the extent of chemical denudation over all the globe. It is based almost entirely upon European data and to a large extent upon inconclusive analyses. Evidence as to the chemical character of the greater American, African, and Asiatic streams was practically unobtainable, and hence we must regard Murray's computation as only a very rough indication of what the truth may be. Data from all the greater river basins of the world are required before we can determine the full significance of chemical denudation.

a Scottish Geog. Mag., vol. 3, p. 65, 1887.

The problem, however, can be attacked locally, with reference to special areas. T. Mellard Reade, for instance, in a well-known investigation, has calculated the amount of solid matter annually dissolved by water from the rocks of England and Wales. Putting the average salinity of the waters at 12.23 parts in 100,000, he estimates that the total annual run-off from the area in question carries in solution 8,370,630 tons of dissolved mineral matter, or 143.5 tons from each square mile of surface. At this rate, by the solvent action of water alone, the level of England and Wales would be lowered 1 foot in 12,978 years.

The figures given in the preceding pages, with reference to American rivers, lead to rather lower estimates. The data may be tabulated as follows, with metric instead of British tons."

Saline matter carried annually to the sea by four American rivers.

The variation, in tons per square mile, between these figures is quite important. The Colorado drains an arid region, and much of the area ascribed to the river adds little or nothing to it. The humid basin of the St. Lawrence, on the other hand, is a liberal contributor of saline substances. The Mississippi, with humid regions to the east and semiarid plains to the west, shows an intermediate figure for the chemical erosion. The mean value, in round numbers 80 metric tons per square mile, is probably not far from the truth, and presumably is fairly correct for the entire area of the United States, exclusive of the Great Basin. This figure, however, refers only to inorganic matter. If organic impurities are to be included, it should be increased by perhaps 10 per cent, that is, to 88 metric tons per square mile.c

Proc. Liverpool Geol. Soc., vol. 3, p. 211, 1876-77. Reprinted under the title "Chemical Denudation in Relation to Geological Time."

2,205 pounds as against 2,240.

For other estimates of the amount of material carried by various rivers, see Geikie, Text-book of Geology, 4th ed., vol. 1, p. 489, 1903. The Thames, for example, carries in solution past Kingston 548,230 tons of fixed inorganic matter in a year. See also the thesis of A. F. White on the waters of Rockbridge County, Virginia (Washington and Lee University, 1906). This thesis deals with North River, a tributary of the James. In Reade's Evolution of Earth Structure still other data are given.

All of these calculations of course are subject to revision, and even the best of them may be greatly modified. At this point a few words of caution may be useful. Suppose we knew exactly how much dissolved matter a certain river annually discharged into the sea. In order to determine its geological significance, we should have to allow for several factors of other than geological origin. Part of the chlorine came in rainfall from the atmosphere and part of it from pollution by towns. The carbonic acid, also, would be partly of direct atmospheric origin, and only a portion would represent the actual solution of limestones. For the chlorine and its equivalent sodium corrections can probably be made; but discrimination in the case of carbonic acid is more difficult. We must also remember that a river drops some of its burden during its course; so that the amount of saline matter delivered to the ocean is not an exact measure of the rock decomposition which its waters have effected.

Reade, in his calculations relative to England and Wales, takes these disturbing factors into account. Spring and Prost, in their work on the Meuse, and Ullik, in his study of the Elbe, have attempted to measure the amount of human contamination. This factor, obviously, must be very variable. In rivers like the Yukon or the Colorado it is negligible; in the Misissippi or the Hudson it is doubtless large.

CHAPTER IV.

THE OCEAN.

ELEMENTS IN THE OCEAN.

For obvious reasons, some of them purely scientific and some utilitarian, the water of the ocean has been the subject of long and elaborate scientific investigations. Considered broadly, its composition is relatively simple and remarkably uniform; studied minutely, it is found to contain many substances."

In his great memoir on the chemical composition of sea water, G. Forchhammer gave a list of the various elements which, up to his time, had been detected in it. The elements which are sufficiently abundant to be determined in ordinary analyses will be considered later; the substances that are less frequently estimated may be briefly considered now.

Iodine.-Chiefly found in the ashes of seaweeds. According to E. Sonstadt, it is present in sea water in the form of an iodate. A. Gautier, examining surface water from the Mediterranean, found iodine only in the organic matter which he separated by filtration, but at depths beyond 800 meters its compounds were detected in the water itself. Living organisms withdraw iodine from solution. The largest amount of iodine, organic and inorganic, reported by Gautier is 2.38 milligrams to the liter. J. Koettstorfer, in an earlier investigation, found much smaller quantities.

P.

Fluorine.-Found directly, and also in the boiler scale of oceanic steamers. A. Carnot's determinations show that the water of the Atlantic contains 0.822 gram of fluorine to the cubic meter." Carles has reported fluorine in the shells of mollusks. Nitrogen.-Present as ammonia, in organic matter, and in dissolved air. The ammonia of sea water has been repeatedly investigated.

For the volume of the ocean and of its contained salts, see ante, pp. 22-23. Phil. Trans., vol. 155, pp. 203-262, 1865. See also J. Roth, Allgem, chem. Geol., vol. 1, p. 400, 1879; and W. Dittmar, Rept. Challenger Exped., Physics and chemistry, vol. 1, pp. 1-251, 1884.

e Chem. News, vol. 74, p. 316, 1896.

Compt. Rend., vol. 128, p. 1069, 1899; vol. 129, p. 9, 1899.

Zeitschr. anal. Chemie, vol. 17, p. 305, 1878.

1 Ann. mines, 9th ser., vol. 10, p. 175, 1896.

• See also earlier determinations by G. Forchhammer and G. Wilson, Edinburgh New Phil. Jour., vol. 48, p. 345, 1850.

Compt. Rend., vol. 144, pp. 437, 1240, 1907.

A. Audoynaud," in water from the coast of France, found 0.16 to 1.22 milligrams of NH per liter. L. Dieula fait," in waters from the Red Sea and the coast of Asia, reports quantities from 0.136 to 0.340 milligram. T. Schloesing found a still larger amount, namely, 0.4 milligram. According to J. Murray and R. Irvine, ammonia is more abundant around coral reefs than in the north Atlantic or German Ocean. It occurs principally as ammonium carbonate, formed by the decomposition of organic matter. Elaborate determinations of ammonia in the Mediterranean are given by K. Natterer. Phosphorus.-Present in the form of phosphates. The phosphatic nodules found on the bottom of the sea are considered further on in this chapter.

Arsenic.-Detected by Daubrée. A. Gautier found its quantity to range from 0.01 to 0.08 milligram per liter.

Silicon. According to J. Murray and R. Irvine, sea water contains silica. The proportion is from 1 part in 220,000 to 1 in 460,000, or even less. The siliceous organisms which abound in the ocean probably take their silica from clayey matter in mechanical suspension. Small amounts of such matter are carried far and wide by currents, often to a great distance from land.

Boron.-Present in sea water and also in the ashes of marine plants. J. A. Veatch," who examined water from the coast of California, found boric acid almost exclusively in samples collected over a submarine ridge, parallel with the land, but 30 to 40 miles away. He suggests for it a volcanic origin from submerged sources.

Lithium.-Reported in sea water by L. Dieula fait. Also detected spectroscopically by G. Bizio in water from the Adriatic.

Rubidium. Found in sea water by Sonstadt. Determined quantitatively by Schmidt, whose analyses will be cited later.

Casium. Also found by Sonstadt.

Barium and strontium.-Can be detected by ordinary methods. Also found in the ashes of seaweeds and in boiler scale. Aluminum and iron.-Easily detected by direct methods.

Compt. Rend., vol. 81, p. 619, 1875.

Ann. chim. phys., 5th ser., vol. 14, p. 380, 1878.

by Marchand and Boussingault.

Dieulafait mentions earlier work

Contributions à l'étude de la chimie agricole, in Fremy's Encyclopédie chimique, 1888.

d Proc. Roy. Soc. Edinburgh, vol. 17, p. 89, 1889.

Monatsh. Chemie, vol. 14, p. 675, 1893; vol. 15, p. 596, 1894; vol. 16, p. 591, 1895: vol. 20, p. 1, 1899.

Compt. Rend., vol. 137, pp. 232, 374, 1903.

Proc. Roy. Soc. Edinburgh, vol. 18, p. 229, 1891.
Proc. California Acad. Sci., vol. 2, p. 7, 1859.
Ann, chim. phys., 5th ser., vol. 17, p. 377, 1879.

See also Thorpe and Morton's anal

ysis of water from the Irish Sea, 1871, cited on pp. 94, 95.