and western edge of the Appalachian Plateau in western New York and northwestern Pennsylvania and Ohio. In those regions the ice moved from a comparatively level plains region into a maturely dissected upland, with the result that its main lines of flow were directed by the north-and-south valleys extending parallel to the direction of ice movement; although the ice did overtop the higher elevations in at least the northern part of the district. The heightening of relief by glacial erosion under such conditions of concentration of ice flow, has, perhaps, its most marked expression in the Finger Lakes region of western New York, where it gave rise to what have been termed "through" valleys. Such valleys extend uninterruptedly through from the St. Lawrence to the Susquehanna drainage systems, the former rock divide between them having been cut away by the ice, so that the divides between north-and-south flowing streams are now illy defined and situated on low morainic or other glacial deposits. The walls of such valleys are steep, their sides straight and they show a marked absence of projecting spurs.19 In some places the steepness is sufficient to make the valley wall a cliff. These valleys have been profoundly modified by glacial erosion, both by deepening and broadening. Not only the main north-and-south valleys, but also the transverse east-and-west valleys show to some extent these effects of ice-scour, and to a less marked degree the tributaries of secondary size reveal the same characteristics. The sides of the valleys are forest-covered, but their broad flat bottoms are all under cultivation. It is clearly apparent that the area of valley agricultural land in this upland region has been increased by the heightening of the relief by glacial erosion.

Glacial erosion, in heightening relief, exerted on general agricultural relations one detrimental effect which, though indirect, deserves mention. It made farm transportation in the eroded plateau district much more difficult. The upland areas are fairly level, and though they are less valuable than the valley lands, they measure a large portion of the area. The trunk transportation lines, the railroads and the markets are in the valleys. The roads from these to the hill farms often need to go straight uphill for from 400 to 800 feet. In some places the grades are so steep as to prevent access to the nearest railroad station. This makes the growing of such bulk crops as potatoes, to which the soils are

19 Tarr, R. S., Watkins Glen-Catatonk Folio, No. 169, U. S. Geol. Survey, 1909, Field Ed., pp. 16, 18, 21, 218, 223.

Fig. 2-Crawford Notch, N. H., from Mt. Willard. Slopes steepened by ice erosion. Photo copyright, 1894, by H. G. Peabody.

adapted, often unprofitable.20 While not in this plateau section, Crawford Notch (Fig. 2) in New Hampshire illustrates beautifully the character of such ice-eroded and steepened slopes. The valley here was also parallel to the general direction of ice movement, northwest to southeast, as shown by the striations, and no doubt20a was similarly carved out by the deeper, main ice currents.

It is perhaps inaccurate to ascribe any increased diversity of relief in the glaciated regions to depositional accumulations, because the morainic ridges, drumlins and other forms of glacial deposits that rise above the general level of the land rest, as a rule, on basement deposits of the same origin, of wider areal distribution and of more level topographic expression. These basement deposits mask the underlying rock topography which, under the moraines. and other elevated forms of drift deposit, may have had a much stronger relief than these give the land at present. As this, however, is only conjectural while the moraines actually exist, some account must be taken of the effect of their elevations and slopes on agricultural operations.

On the map, Fig. 3, are indicated the positions of the morainie belts and drumlin areas of the eastern agricultural part of North America. This map, however, exaggerates the relief distribution of such forms because the width and continuity of the bands as shown is too great, and because comparatively level lands are included within the tracts delineated as morainic and drumlin areas. While some of the morainic masses rise to heights of 150 to 300 feet and are distributed over zones three, five or even fifteen miles in width, making an exceedingly irregular topography, others are little more than broad, smooth, masses, rounded banks of drift."1 Drumlins also vary from massive hills 100 to 200 feet high, which may be three or four miles long, to indefinite swells in the drift surface. In Europe, moraines are conspicuously developed only in south Norway and Sweden, on the Baltic Ridge of northern Germany and in Finland and West Russia. Drumlins occur in Ireland and Scotland but only sparingly, if at all, in continental Europe.

Considered as topographic irregularities the occurrence of the larger moraines and drumlins must on the whole be counted as a detriment to agriculture in that their slopes are often too steep

20 Warren, G. F., and K. C. Livermore: An Agricultural Survey. Agri. Exp. Sta. of the College of Agric., Cornell Univ., Bull. 295, pp. 437, 458, 560.

20a Since this paper was written J. W. Goldthwait in an article, "Glacial Cirques near Mt. Washington," Amer. Journ. Sci., Vol. XXXV, Jan. 1913, p. 12, cites Crawford Notch specifically as a probable example of a glacially steepened "through valley."

21 Chamberlin, T. C., in Geikie, J.: The Great Ice Age, 3rd Ed., London, 1894, p. 741.

for cultivation, and in that the irregularities of a well-developed morainic or drumlin zone make it difficult country to bring under the plow. But since the relative area occupied by moraines of such strong expression is small, the loss due to this is probably not great. Where the moraine is developed in broader, lower tracts of thickened drift its slightest slopes often promote good drainage conditions without interfering with tillage operations. Soils on drumlin slopes are usually well drained and in New York are well adapted to fruit trees, especially apples and cherries.22 On the other hand the depressions of a typical kettle moraine area, low-lying pockets with rims uncut by drainage gaps, are consistently shunned by fruit growers and truck gardeners because they have poor air drainage. The cold, heavier air slides down the slopes and collects at the bottom of such pockets, as they have no outlets at the lower levels.

(b) Modification of Relief and its Agricultural Consequences. In the literature descriptive of regional glaciation occur a multitude of references to the effect that the ice invasions resulted in a general reduction of the preglacial relief and that this was accomplished both by glacial erosion and by deposition of drift. In order to understand why this should be the case it is necessary to consider for a moment the nature of the preglacial topography in representative areas and the way in which such topography would be affected by glacial processes.

Processes of weathering, and the erosion of running water, tend to etch the land surface into an intricate relief pattern, bringing into topographical prominence all structural and petrographic differences that may exist in the bed rock of a given region. While the beginning and end stages of a normal cycle of erosion are marked by relief of little expression, it must be remembered that the youthful stage is of very short duration, and that undissected peneplains are practically non-existent in the geological present. Some phase of the middle stage of normal topographic maturity is common on the land surfaces of the globe.

While it cannot be maintained that the preglacial erosion surfaces of the regions invaded by the continental ice sheets had all been developed to a typical stage of maturity in the normal erosion cycle, it is true that the plains areas of both Europe and America that were covered by the glaciation had a much more diversified

22 Whitney, Milton: Use of Soils East of the Great Plains Region, U. S. Dept. of Agric., Bur. of Soils, Bull. 78, p. 106.