[43] In1927 a General Map of the Soils of Europe was  published, giving the results of investigations made under the auspices of the International Society of Soil Science. ⁽¹⁾ It is particularly useful for this study as its soils regions are effectively simplified and allow a quick comprehension of the relations between regions of soils, climate, and vegetation in northwestern Europe (See Fig. 8 and compare with Figs. 2, 6, 7, and 9).
 

One is struck by the great stretch of "moderately podsolised forest soils" ⁽²⁾ running from interior Asia, south of 60 degrees latitude, [45] along the coasts of the Baltic and North seas (not including the peninsula of Jutland), through northern and western France, the Pyrenees, the Cantabrians, Galicia, and the Minho Province of northwest Portugal. Only the western portion of this area is shown in Figure 8. To the south of the Minho Province a [46] wide band of these soils extends along the humid interior upland of Portugal, reaching approximately to the Tejo River, but along the Atlantic Coast the Douro River marks its southem limit. This soils area can be equated with the area of oceanic influence, abundant rainfall, relatively mild temperatures, and mixed-forest vegetation.

In sharp contrast are the soils of the meseta, lying to the lee of the northern and northwestern mountains of Iberia, where wide areas are covered with brown forest soils or bright chestnut-colored dry forest soils, bespeaking the drought of the interior.
 

One of the contributors to the map of 1927 was Emilio H. del Villar, who presumably was responsible for the Iberian area. After that publication, however, he continued his work and in 1937 published a volume wholly devoted to the soils of the Iberian Peninsula. ⁽³⁾ In this text and its accompanying map he makes far more detailed specifications for the soils regions. In fact, the amount of detail makes this map less useful than the earlier, more generalized map of 1927. The text, however, is helpful, even though at first glance it seems to contradict his findings as published in the report of 1927. For example, the great area, mentioned above, of "moderately podsolized forest soils" is broken up into subareas, in terms of parent materials. The assumption is that here the parent materials were more important in the ultimate nature of the soils than was climate. ⁽⁴⁾ Those developed from granites are different from those derived from Silurian schists. Both of these are in separate categories from the soils derived from the calcareous Mesozoic materials.

[47] From the Pyrenees to S. Vicente, thirty miles beyond Santander, is an almost solid zone of the "general occurrence of humid siallitic soils." From S. Vicente to Oviedo is an area where most of the soils are derived from calcareous materials. To the south of this zone, and intermingling with it, are "humid siallitic soils." To the west of Oviedo is a great zone of "the general occurrence of the acid-humic type soils," which extends through Galicia, North Portugal and along the humid highland interior of the Beiras to the Tejo River In spite of Del Villar's differentiation according to parent materials, the great soil areas indicate their intimate association with climate. Even the area of soils derived from calcareous rocks is now broadly similar to its neighboring areas, for under the climatic conditions of the rainy lowland the soils have been largely decalcified. ⁽⁵⁾ In general, all of these soils can be associated with Marbut's pedalfers. ⁽⁶⁾ They are acid in reaction, but not to the degree that would inhibit a healthy forest growth. ⁽⁷⁾
 

Within the angle of the northern and western mountains appears a zone of "intermediate siallitic soils" Farther inland begins the great zone of "xero siallitic soils," which broadens southward. In the interior areas the pedalfers become less and [48] less acid as the elevations decrease and the land is drier, toward the Iberian interior. At Zamora on the west, and to the north of Burgos, begin the areas of pedocals that cover most of eastern Spain and most of the area to the south of the Sierra Morena.
 

A large proportion of the acid-humic soils of the northwest occur at present in what Del Villar calls the "agropedic phase." The differences between them depend upon cultivation, improvement, and manuring. The Portuguese say that these soils are man-made. This situation seems to be a feature of areas where farming practices inherited from northern and Central Europe have been common since remote ages. Del Villar says:

. . . the acid-humic soils are commonly considered poor; but it is necessary to qualify and adjust this judgment. . . . within this acidhumic region there are areas of agricultural production generally more intensive than that of the dry lands of the peninsula. . . soils of the same type dominate the greater part of the British Isles, Holland, North Germany, and Denmark, countries which show the most intensive agricultural production in Europe. ⁽⁸⁾

The province of Trás-os-Montes lies east of the mountain barrier that limits the Minho Province. It is politically Portuguese because of its geologic and tectonic history, which has partially isolated it from Spain and has allowed more convenient communications with the west. In other ways it is more Spanish than Portuguese. Its soils have more the quality of those of León than those of the Minho. In the north of Trás-os-Montes and through much of the Spanish province of León are found "intermediate siallitic soils" (according to the Del Villar terminology) , ⁽¹⁰⁾ and in this relatively dry area, parent-material differences are strongly reflected in the soils. The hard mica schists do not break down readily, and because of this fact there are large areas of shallow and essentially rocky soils ⁽¹¹⁾ that support only a meagre heath. Other schists, somewhat more friable, break down more readily, the reflection of which can be seen in the easily established forest growth. ⁽¹²⁾ Southern Trás-os-Montes is characterized by the "general occurrence of xerosiallitic soils," that is, soils with neutral reaction and low organic content, which develop under conditions of relative dryness and from siliceous parent materials. They cover not only southern Trás-os-Montes but also an enormous area of the [50] interior of Spain (the provinces of Salamanca, Cáceres, and most of New Castile, east to Ciudad Real) , as well as most of the Alentejo in Portugal.
 

There are two other relatively dry areas of Portugal where soils reflect the parent material. These appear distinct on the Del Villar map by reason of their calcareous rock. This is a situation very different from that of the calcareous area of the humid north, to the east of Oviedo, where the lime is effectively leached. The larger of the two areas is clearly delimited on the east by the Lisbon-Tomar-Coimbra-Espinho line. Dominant within the region are terra rossa soils. This term is commonly used by European pedologists to describe a calcareous soil stained red by iron oxides, which is favored in development by the Mediterranean climate with its pronounced wet and dry seasons. The second area of terra rossa soils is that lying to the north of the Algarvian littoral. Under Algarvian rainfall conditions the limestone is not decalcified, and in many places the parent material is exposed at the surface, loose material on top being carried away as fast as it appears. Limestone rock and terra rossa soils reach to the sea in the western half of the southern coast.

Against the northern region of limestone lies the great quadrilateral area of dunes, and the eastern half of the Algarvian coast is likewise a distinct area of sand deposit. Such areas are shown on the Del Villar map as being of "sandy-skeletal coastal soils."
 

In spite of the differences between subareas indicated by Del Villar, the fact remains that from the French border at the western end of the Pyrenees to central Portugal there is a great, unbroken stretch of either "humid siallitic" soils or of [51] those pertaining to the series next to it in order of acidity, the "acid-humic" soils. According to the United States' classification, all would fall into the category of moderately podsolized soils, which brings us back, essentially, to the classification of Stremme.⁽¹³⁾ Whichever classification or map is used, the general fact emerges that the great soils areas are in accord with the regions of climate of northern and western Iberia. The humid peripheries are clearly set apart, in soil types, from the dry interior and the south of the peninsula.

1. General Map of the Soils of Europe, 1927, by the Sub-Commission for the European Soil Map of the Fifth Commission of the International Society of Soil Science, Chairman, H. Stremme, Danzig. German text published in Danzig, 1927. Translation by Dr. W. G. Ogg, 1929.

2. A podsol is a soil developed in cool, moist climates under forest vegetation, commonly coniferous. It is leached in its upper layers and is usually strongly acid. Highly siliceous materials are most susceptible to podsolization. The soil has a characteristic grayish-white color. Soils and Men, Yearbook of the United States Department of Agriculture, 1938, pp. 972, 1020.

3. Emilio H. del Villar, Los Suelos de la Península Luso-Ibérica.

4. Ibid., p.67.

5. Ibid., p. 199.

6. Ibid., p 32. Marbut former chief of the United States Soil Survey distinguished between two great soil groups in terms of the accumulation of carbonate of calcium or the lack of such accumulation. The first he named "pedocals," using the Greek pedo (ground) plus Latin calcis or calx (lime). They are associated with dry or relatively dry areas. For the other great group he coined the name "pedalfer," using the same Greek prefix but adding the first two letters from alumen and ferrum, the Latin words for aluminum and iron respectively The pedalfers usually show not only the lack of a zone of lime accumulation but the positive accumulation of iron and aluminum compounds They are to be associated with humid areas See Soils and Men Yearbook of Agriculture USDA 1938 p. 982.

7. H Gaussen, "Le Milieu physique et la forêt au Portugal," Revue Géographique des Pyrénées el du Sud-Ouest, XI, Nos. 3-4 (1940), 240.

8. Del Villar, Suelos de la Península, p. 66.

9. J. Leite de Vasconcellos, Origem histórica e formação do poyo Português, p. 15.

10. Del Villar, Suelos de la Península, III. He says that these are approximately the braunerde of Ramann, and Robinson calls them brown forest soils. According to the classification in the United States they would be listed as the most acid of the "non-calcareous pedocals" or "non-calcic brown soils." This is according to the information supplied by Raymond E. Stone, Department of Soils, University of California, Berkeley, California. Mr. Stone has recently spent several months in areas of the western Mediterranean studying soils and their distribution

11. Del Villar calls them "oropedic," so-named because they appear most frequently in mountains. In such soils the A horizon lies directly upon the C horizon, or parent material. Del Villar, Suelos de la Península, p. 33.

12. Gaussen, loc. cit.

13. For Portugal only, a useful map of soils has been elaborated and published under the direction of Luis Bramão, "Carta dos Solos de Portugal," Estação Agronómica Nacional, Direcção Geral dos Serviços Agrícolas. It is not serviceable for this chapter, as it does not show extensions of the soils regions beyond the political limits of Portugal.