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vantages, favorable to agriculture, other than that of simply greater initial content of mineral plant food.

(b) Variation in Age of Glacial Soils with respect to Crop Productivity. From what has been said above, it may be gathered that the geological youth of the glacial soils is a factor of importance in determining their superior agricultural worth. The original, undecomposed nature of the glacial soil particles, rock flour, and the short time they have been exposed to weathering processes are in part responsible for their so-called lasting and strong qualities in contrast with weaker, non-glacial soils. This distinction may be extended farther to include differences between the glacial soils themselves, according to the relative ages of the glaciations during which they were deposited. Thus Hopkins32 has shown that, in the several glaciations which have, in the main, given rise to the soils found in Illinois, there is a progressive increase in the mineral plant food content of such soils from the oldest to the youngest. Moreover, a very real difference exists in the actual productivity of the soils of the early and late glaciations, whether or not this depends on the mineral plant foods present in them. Hubbard shows this very strikingly by contrasting the agricultural conditions in the north-and-south adjacent Coles and Cumberland Counties of Illinois, the former lying almost wholly within the Early Wisconsin glaciation, while the latter has a Lower Illinoisan glaciation soil-cover over the greater part of its area. Land values in Coles County at the time the article was written ranged between $75-$125 per acre, with the average above $75; while in Cumberland County (with the older Illinoisan glaciation soil-cover) the prices were between $15-$40 with the average near $30. According to the 1910 census31 average farm values in Coles County were $125 per acre and over, while in Cumberland County they ranged between $50 and $75 per acre, yet in both counties 90-95% of the land was found to be in farms. According to Hubbard again, the value of crops, per acre of improved land, was from $10-$15 for Coles County and from $6-$10 for Cumberland County.

It may be that these differences in productivity should be ascribed to conditions of physiographic, rather than geologic youth and age, for in Coles County tile drainage is practiced, rich swamp

32 Hopkins, C. G., and Pettit, J. H.: The Fertility in Illinois Soils, Univ. of Ill., Agric. Expt. Sta. Bull. 123, pp. 201-202.

33 Hubbard, Geo. D.: A Case of Geographic Influence upon Human Affairs, Bull Amer. Geogr. Soc., Vol. XXXVI, 1904, pp. 145-157.

34 Bulletin Thirteenth Census of the United States, 1910: Agriculture, Illnois, map p. 2.

lands are thus reclaimed, while in Cumberland County such drainage is useless, primarily because tributaries to main natural drainage streams are developed in so much greater numbers as to make the map of Cumberland County appear darker. Thus relative dissection of the glacial deposits themselves apparently makes for differences in crop productivity irrespective of differences in mineral plant food content. Leverett 35 makes clear the very strong contrasts in this respect which appear between the deposits of the different glaciations. "In the Illinoisan glacial drifts of western Illinois approximately one-half the surface has been reduced below the original level as a result of post-Illinoisan glaciation drainage. development; while in the Wisconsin drift, post-Wisconsin drainage has scarcely sufficed to reduce one-tenth its original surface." In connection with such weathering and dissection the older glacial soils may have also undergone structural and textual modifications detrimental to fertility. As the youngest glaciations did not extend so far south and east in Central Europe as did the earlier ones it is possible that these glacial lands would show, if an exact comparison could be made, because of their greater age, an average lesser productiveness than do the younger glacial deposits which cover so large a part of the area of the central United States and southern Canada.

(c) Textural Variations of Glacial Soils in relation to Diversified Agriculture. In its broadest sense the term, intensive agriculture, implies the utilization both of the land and the labor of the man on the land to their utmost extent and according to the best methods and with the best equipment possible. Fulfillment of these conditions involves continual occupation for the labor on the farm. In order that this may be possible a variety of tasks to suit the different conditions of weather and season must be available; accordingly a variety of crops must be grown so that the work does not all come at once. In other words, diversified, as well as intensive agriculture, must be practiced to get the greatest possible economic advantage from the land. Even in regions where intensive agriculture, in the more restricted sense of specialization in one crop, is unprofitable, the opportunity for a diversified agriculture is important, for it means the possibility of producing a large proportion of the variety of foods demanded by the human and animal labor on the farm itself, where field crops are extensively raised for

35 Leverett, F.: Weathering and Erosion as Time Measures, Amer. Jour. of Science, Vol. XXVII, 1909, pp. 356-7.

a money return. Therefore, if the soil over a large area is restricted, texturally and in other characteristics, to a very narrow variation in type, adapted to only a comparatively few crops, such uniformity in soil type is necessarily a detriment to both intensive and diversified farming. This is an economic disadvantage, as, with increasing density of population in civilized countries, a more and more intensive and diversified agriculture must be practiced.

According to present knowledge different plants are more adapted to textural variations than to variations in the other known characteristics of the soil. On the other hand this adaptation of plants to certain soils is often so marked that it has been proposed to classify soils according to their natural typical plant growth. Crops also are adapted to certain soils. A compilation made from a wide range of agricultural literature showed that among others the following crops could be grown in largest quantity and in some cases also of best quality on the textural soil type indicated:

Clay-wheat, timothy, blue grass.

Silt loam-corn, apple.

Loam-red clover, alfalfa, field beans.

36

Sandy soils-potato, field peas, turnip, barley, rye, buckwheat, peach.
Calcareous soil-white clover.

Muck soils-celery, cabbage, lettuce, onions.

This list includes only such crops as show marked adaptation. It could be much extended if others were included that, other conditions being equally favorable, thrive best on certain soil types.

The application of the above paragraphs is found in the wide variety of conditions which attended the deposition of material by the ice during the retreat of the continental glaciers, giving rise to a great diversity in soil types. A list of the different forms of glacial deposit to which distinctive names have been given will almost suffice to show how wide the range in texture is. Often, moreover, these forms intergrade in a manner most puzzling to the glacial physiographer who attempts to map them, such combinations adding further complexity to the soil texture in the glaciated regions.

Conspicuously developed terminal, recessional and lateral moraines are commonly stony, with a filling of gritty clay between the boulders. Though large boulders may not predominate the materials composing their ridges are typically coarse, sandy and

36 By Dr. Bouyoucos, formerly of the N. Y. State Agric. College at Cornell University, soil seminar, March 20, 1911.

gravelly, in general unfit for cultivation. In the central plains and prairie region of the United States such morainic masses are commonly given over to farm wood-lots and pasture land. Similarly the coarse stratified material of kames and eskers and their steep topography unfits them for the plow and they are generally timber-covered so that it is difficult to obtain good photographs showing the sinuosities of an esker course. Drumlin forms are equally steep but have better soils texturally; they are, therefore, generally under cultivation. Much more extensive in area over the glaciated regions than the conspicuous ridge deposits of moraine, kame, esker and drumlin, are the lower, more massive moraines, the ground moraine and the till sheet. These forms can not be sharply differentiated in the field. They grade into one another. In general they comprise the material deposited by the ice during periods of slow but essentially continuous melting back. Under such conditions the thin wedge at the front of the ice may be conceived of as fairly clogged with debris, super-, en- and subglacially, a concentration of all the stuff distributed through a much greater thickness of ice back from the front. Away from hilly and mountainous regions this material was probably mainly massed in the lower ice layers, the cargo acquired by erosion and abrasion in the long journey from the centers of ice dispersion. In regions of greater relief, where ridges and summits projected far up into the body of the ice currents, or even through them, in the waning stages, englacial and superglacial material amounted to a much greater bulk of the deposits laid down. Thus the till sheet (embracing in that general term the low massive moraines and the ground moraine) varies in composition from the thin bouldery deposits of the New England uplands (where it has been estimated that in some parts it took on the average a month's work for a man to remove the large stones from each acre to get it ready for plowing) to the deep, fine textured aggradations of the plains areas, derived from prevailing soft rocks, converted into rock flour by glacial grinding under the sole of the ice, and extending now practically level and unbroken over miles of area. Although such extremes in texture occur in these deposits of similar origin the till sheet on the whole supplies a prevailingly fine soil. Of the approximately 24,000,000 acres of area covered by such glacial material that have been mapped in the United States by soil surveys, about 73 per cent. has been found to come within the narrow textural range of loam, silt loam and clay loam. These are all heavy soils adapted to general farming, and they have been desig

nated the great wheat and corn soils of the country.37 The smaller areas of coarser, lighter soils, sandy in texture, associated with the loam soils, and part of the same deposits in origin, are well adapted to fruit and vegetable growing, though not yet utilized to their fullest extent. Thus while plenty of opportunity is afforded for variety of crops, the greater proportion of such lands is specially adapted to the growing of the two grains which are staple foods for man and beast.

The surface portions of the till sheet deposits no doubt owe their prevailingly fine texture in part to postglacial weathering, but, in part also, to the influence of outwash waters depositing fine particles between the larger morainic fragments. When the outflowing glacial waters were of greater volume and faster flow, coarser particles could be carried and deposited away from the ice front. Of such origin are the sand plains, outwash gravel aprons, glacial river terraces and valley trains. But associated with these coarser soils are found areas of very fine grained and dense lake clays, deposits in quiet waters of temporary or higher level lakes and ponds of the glacial period. These outwash and lake bottom soils have in general a lower topographic position than the other glacial material, consequently they are nearer the level of the underground water table. This often insures them a water supply where in other positions such coarser soils would drain and dry out too rapidly. Consequently a heavier type of crops can be grown on many of these soils than would otherwise be possible. The sorting action of water has further resulted in a separation of a much greater number of textural grades of soils than in the till-covered areas, and has arranged them in much more definite groups and bands. This combination of conditions gives a great opportunity for specialization in different crops within comparatively narrow areas. On the lake clays wheat, hay, oats and grapes thrive. The clay loams are available for intensive dairying, as they are unexcelled grass lands, and are also adapted to wheat. The loam group, including gravelly and stony loams, is perhaps the most typical of the soils of this region; such are very important for 'canningvegetables, producing large yields of fine, firm quality. (Fig. 5.) These are also some of the best fruit soils, especially for apples and pears. Sugar beets and tobacco do well on the sandy loams, as do also peaches. The sandy soils are best for potatoes, strawberries and early vegetables.

37 Whitney, M.: The Use of Soils East of the Great Plains Region, Bur. of Soils Bull. No. 78, pp. 95 and 129, U. S. Dept. of Agric.

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