drift deposits of such strong expression are not, however, of great areal extent.

(d) The extensive leveling, both by glacial erosion and drift deposit, of the minor rugosities characteristic of the normal, mature stage of development of preglacial relief constitutes an extremely favorable influence on agriculture resultant from ice invasion. Flat, upland, interstream areas may in some instances have suffered by modification of relief, in that their residual soils were eroded and only thin, stony soils left in their place by the ice.

(e) The average great thickness of the drift deposits and their level topography conserve the ground water supply of the glaciated regions.

(f) Glacial soils are more fertile than non-glacial soils; in part because they contain a higher percentage of the soluble mineral plant foods. Great commingling of different rock materials in glacial soils gives more uniform composition and fertility to them than is characteristic of sedentary soils. The level topography of glacial drift plains soils resulted in a deep accumulation of organic matter, which contributes much to their agricultural worth. The dominant textural quality of glacial soils is that best adapted to the production of the staple food crops.

(g) The deposits of the younger glaciations which cover the larger part of the ice invaded regions of central North America. have a greater crop productivity than the older glacial soils.

(h) Owing to the wide variety of conditions attending the deposition of glacial drift, many textural soil types occur in the glaciated regions, providing for diversified and intensive farming within narrow areal limits. The more valuable non-glacial soils are quite apt to be uniform in texture over wide areas.

(i) Loessial soils extend the favorable influence on agriculture, due to glaciation, beyond the limits of the ice advances. Some of the non-glaciated areas would probably show even more marked agricultural deficiency, as compared with the glaciated regions, if these loessial soils were not present.

(j) In the humid agricultural section of eastern North America from 16 to 20 per cent. of the glaciated areas is unavailable for agriculture because submerged under glacial lake waters. This loss is offset, perhaps in very large measure, by the modifying in

fluence of such bodies of water on climate. This climatic protection especially favors the production of valuable fruit crops.

(k) The level topography, uniform soil texture, the deep humus cover, and often the great areal extent of deposits on drained and filled glacial lake basins affords a soil of great fertility and very susceptible to cultivation by mechanical power. By such utilization of machinery on these areas and, also, on the level till plains, the labor cost of grain production has been very materially reduced. In conjunction with the muck deposits, characteristic of the filled basins of the smaller glacial lakes, are often found marl deposits. These may be used to advantage to correct possible acidity in the muck, in which very profitable crops of vegetables may then be grown.

6. CONCLUSIONS

The beneficial effects on agriculture, due to glaciation, are of wide variety and apparently outweigh detrimental influences due to the same cause. As a net result, glaciated lands are, therefore, of greater agricultural value and utility than non-glaciated areas under otherwise essentially similar conditions. It is not feasible, however, to state numerically the order of this difference, because too many unwarranted assumptions would need to be made.