over the pine forest during fourteen months was 33.1 inches; that over a sandy plain, at a distance of 1.9 miles, only 29.9. Of that which fell on the forest only 18.6 inches reached the ground. But through the influence of the trees, moss, and fallen leaves, the evaporation was so decreased that the forest soil retained a good deal more of the rainfall than the open lands. Among the important general inferences from these observations are that forests (1) tend to equalize extremes of temperature; (2) act as condensers of atmospheric moisture, and hence (3) increase deposition of dew on neighboring lands and (4) attract more rainfall; (5) prevent part of this from reaching the soil; (6) enable the soil to retain much better what it does get, so that it has more for future supply of springs and streams than the open land, (7) and thus tend to prevent both floods and drouth. These conclusions apply with especial force to evergreen forests. The economy of nature in covering sandy and calcareous regions with forests of pine thus becomes clearly apparent.

THE SOIL IN ITS RELATIONS TO VEGETABLE PRODUCTION. Agricultural Geology.

The science of agricultural geology, or, as some of its followers prefer to term it, geognosy, has received a new impetus in the researches and publications of Professor Orth, of the Agricultural Institute of the University of Berlin. Besides his valuable prize essay ("Die Geognostisch-Agronomische Kartirung") Professor Orth has lately published a series of six charts, each giving six diagrams in profile of the characteristic sedimentary soils of North Germany. They show the different strata of surface- and sub-soil, their thickness and other characters, down to a depth of three meters—about ten feet. These, with the investigations upon which they are based, illustrate most forcibly how incomplete a measure of the value of a soil can be furnished by chemical analysis alone, and how extended studies and observations are necessary to a full knowledge of the factors that decide its fertility.

New Jersey Marls.

The annual report of the New Jersey Board of Agriculture for 1876 devotes some eighty-four pages to a descrip

tion of the geological characteristics, chemical composition, and agricultural uses of the marls of that state. The general conclusions as to the agricultural value of the greensand marls which are the most important are, in substance, that (1) those containing the largest percentage of phosphoric acid are the most valuable; (2) those rich in carbonate of lime are the most durable; (3) the potash in them has but very little, if any, present value, it being combined with silica, and hence insoluble; (4) the greensands, containing but little of either phosphoric acid or carbonate of lime, become active fertilizers when composted with quicklime; (5) the injurious effect of sulphate of iron in the marls can be counteracted by composting with lime; (6) the crops particularly improved by them are all forage crops (grass, clover, etc.), potatoes, buckwheat, wheat, rye, oats, and corn. The Tertiary and calcareous marls seem to be very useful, but less so than the greensand.

Percolation of Water through the Soil, and Consequent Loss of Plant-Food.

The Scientific Farmer reports some very interesting and instructive experiments by Dr. Sturtevant on the relation between the amount of water which falls in rain and that which percolates through the soil. These are made by means of a lysimeter with an area of one five-thousandth of an acre, on the plan of those performed at Rothamstead, in England, and other places in Europe. The soil was a gravelly loam. The total rainfall during the year 1876 was 43.88 inches, of which only 4.76 inches leached through to a depth of twentyfive inches. That is to say, only 11 per cent. of the total amount of water which fell percolated to this depth; while in European experiments (under varying conditions of soildepths at which tests were made, etc.) the percentage of percolation varied from 20 to 42.5 per cent. Dr. Sturtevant infers that the waste of fertilizing elements from New England soils by drainage must be much less than in England.

Loss of Plant-Food through Rivers.

Breitenlohner and Harlacher calculate that the river Elbe, which takes up all the Bohemian rivers, and carries off five milliards of cubic meters of water per annum, takes with this

455,950 tons of suspended matters and 518,900 tons of dissolved matters-making, in all, 974,850 tons. This includes some 117,000 tons of lime, 23,440 tons of magnesia, 45,430 tons of potash, 33,000 tons of soda, 21,100 tons of chloride of sodium, 38,080 tons of sulphuric acid, and 1250 tons of phosphoric acid (Dingl. Polyt. Journal, ccxxiii., 328).

Soil-Absorption.

One of the most important factors of the fertility of soils is their faculty of absorbing the ingredients of plant-food from their solutions, and retaining them for the use of plants. In a new work by Detmer on soils ("Die Naturwissenschaftlichen Grundlagen der Bodenkunde"), 60 pages, and in Thiel's "Landwirthschaftliches Conversations-Lexikon" (Agricultural Encyclopædia) now being issued, 12 pages, are devoted to the discussion of this subject. Detmer gives conclusions essentially as follows:

1. Ammonia, potash, lime, magnesia, sulphuric acid, silica, and phosphoric acid may be absorbed by soils. Nitric acid and chlorine are not absorbed to notable extent.

2. When these substances are supplied in the free state to a soil, they enter into combination with its ingredients. When a base is absorbed by the soil, from a salt in solution, an equivalent amount of another base leaves the soil, and goes into the solution.

3. The soil absorbs a given ingredient of a salt most energetically when the other ingredients of the salt are at the same time recombined.

4. From very dilute solutions nothing is absorbed.

5. The time of contact between soil and solution does not essentially affect the amount of absorption.

6. The absorption is increased by heat, and is peculiarly affected by the amount of soil and the amount and concentration of the solution. Nos. 4 and 6 refer more especially to the observations made in laboratory experiments.

Heiden, the author of the article on Absorption in the Encyclopædia referred to, who has himself made a good many experiments upon the subject, arrives at conclusions not widely different from those of Detmer. He shows, however, that the absorption of sulphuric acid is very slight.

As to the question in how far the elements that have been absorbed by the soil may be redissolved and carried away again, Heiden states

(1) As to bases. The bases do not become entirely insoluble by absorption, but the amount of water required to redissolve them is far greater than that in which they were originally dissolved. The force with which the soil holds the absorbed base is far greater than that which the water can exert to remove it.

(2) As to acids. Phosphoric and silicic acids are, like the bases, redissolved to slight extent, but require for this purpose very large quantities of water. Sulphuric acid is absorbed but little; nitric acid and chlorine scarcely at all; and all three, but especially the two latter, are very easily removed from soils by water.

The Causes of Soil-Absorption

Have been much discussed and experimented upon. The main questions in dispute are as to how far they are physical, dependent upon surface attraction; how far they are chemical, due to chemical combination; and what ingredients of the soil and what special circumstances decide the absorption. The absorption of phosphoric acid seems to be a chemical process dependent upon its combination with lime and magnesia, and more especially with iron and alumina. The absorption of silica seems likewise to be due to chemical combination, particularly with lime and alumina, to be decreased by humus, and hence greatest in soils containing little organic matter.

The Absorption of Bases by the Soil

Has been lately studied by H. P. Armsby, with a view to gain light upon the question as to how far this is due to chemical and how far to physical causes. The view that the prime cause of the absorption is a physical one-surface attraction-has been held by several experimenters, as Liebig, Henneberg and Stohmann, Peters, and Brustlein; while the investigations of Way, Eichhorn, Rautenberg, Heiden, Knop, Warrington, and Pilitz show clearly that chemical changes are involved. The prevailing opinion has been that these chemical changes consist mainly in the exchange of

bases of hydrous silicates in the soil for the base absorbed from the solution, though several have considered that the oxides of iron and alumina, and some organic compounds, play a very important rôle. Armsby concludes from two series of experiments, one with soils and the other with hydrous silicates, that "the absorption of combined bases by the soil consists in an exchange of bases between the salt and the hydrous silicates of the soil; and that this exchange, which is primarily chemical, is only partial, its extent varying-1st, with the concentration of the solution; 2d, with the ratio between the volume of the solution and the quantity of the soil used."

"The cause of these variations is probably the 'action of mass,' or the tendency of the resulting compounds to re-form the original bodies, the absorption actually found in any case marking the point where the two forces are in equilibrium" (Am. Jour. Sci., XIV, 1877, p. 25).

On the whole, the results of later investigation seem to lead towards the conclusion that the cause of the absorption of acids is mainly, if not entirely, chemical; that of bases, partly physical but chiefly chemical.

Oxidation of Nitrogen Compounds in the Soil.

To test the action of organized ferments upon the oxidation of nitrogenous compounds, Schloessing and Müntz filled a wide glass tube, a meter in length, with ignited sand mixed with 100 grams of powdered chalk. The mixture in the tube was watered every day with a fixed quantity of sewage. After twenty days nitric acid appeared in the water flowing from the bottom of the tube, and increased rapidly until the last trace of ammonia disappeared. After four months chloroform was passed through the tube to kill the ferments. The formation of nitric acid ceased at once, and did not begin again until fresh germs, obtained from land possessed of marked nitrifying properties, were sown in the sand. It is thus shown that nitrification may be caused by organized ferments; and that a sandy and barren soil, if it contain enough lime to neutralize the nitric acid, may serve admirably for the purification of sewage.