These figures tell of the hard conditions of life characteristic of most mountain regions. Population under normal circumstances settles in the narrow valleys between the ranges and along the borders of their drainage stream. Soon, however, the food supply becomes inadequate for the growing numbers, so that artificial means have to be employed to expand the area of arable land. The soil on the mountain slopes is so thin that it yields only a scanty return to the labor of tillage. Moreover, under the operations of ploughing and harrowing, it is exposed to the danger of washing; so that after a few croppings the underlying rock of the mountain side may be laid bare, and all that was valuable in the quondam field deposited in the valley as silt or swept away to enrich the distant delta of the nearest trunk river.
To obviate this difficulty and to secure the desired increase of arable land, mountain peoples the world over have resorted to terrace agriculture. This means hand-made fields. Parallel walls, one above the other, are constructed on horizontal lines across the face of the steep slopes, and the intervals between are filled with earth, carried thither in baskets on the peasants' backs. The soil must be constantly renewed and enriched by manure in the same way, and the masonry of the retaining walls kept in repair. Whenever possible these costly terraced fields are located by preference on southward facing slopes, where the tilt of the land makes the fields catch the rays of the sun almost at right angles and thus counteracts the chill of the higher altitude, while the mountain behind protects the growing crops from cold northern winds. Good arable land, being limited in amount, commands a high price; and especially do choice terraced fields in vine-growing countries, since they make the best vineyards. Such fields in Switzerland will bring from $300 to $2,000 an acre, and are estimated to produce annually two bottles of wine for every square foot.[1267]
Geographical distribution.
Terrace agriculture, rare in new countries, in the more densely populated Old World is widely distributed in mountainous areas. In Germany, where it is nearly identical with the culture of the vine, it is found along the steep slopes overlooking the valley of the Moselle and the Rhine; also in the Vosges Mountains, the Black Forest and the Swabian Jura, to the limited altitude in which the vine will flourish in these northern regions. In the Alps it is widespread, and not confined to the culture of the vine. The traveler passing along the upper Rhone through the sunny Canton of Valais follows these terraced fields almost as far as Fiesch (altitude 3458 feet), beyond which agriculture proper becomes more and more restricted on account of the elevation, and passes rapidly into the mere hay-making of a pastoral community. Between Leak and Sierre, not only the mountain sides, but also the steep gravel hills constituting the old terminal moraine deposited by the receding Rhone glacier across the valley floor, are terraced to their very tops.
Terrace cultivation prevails in the mountains of Italy; it is utilized not only for the vine, but for olives, maize, oats, hemp, rye and flax. On the gentler declivities of the Apennines, the terraced walls are wider apart and lower than on the steep slopes of the Ligurian Apennines and along the Riviera of the Maritime Alps, where the mountains rise abruptly from the margin of the sea.[1268] Careful and laborious terrace cultivation has produced in Italy a class of superior gardeners. The Genoese are famous for their skill in this sort of culture. The men from the Apennine plateau of the Abruzzi readily find positions in the lowlands as expert gardeners.[1269]
Terrace culture of the Saracens.
The Saracens of Spain in the tenth century converted every mountain slope into a succession of green terraces. They built walls of heavy masonry, and brought water, loam, and fertilizing materials from great distances. The slopes of Granada back of Malaga and Almeria were covered with vineyards. Every foot of land susceptible of cultivation was turned to account, every drop of water from the ill-timed winter rains was conserved for the growing season. The application of intelligence and labor to tillage enabled the Hispano-Arab provinces to support a dense population.[1270] These Saracen cultivators had come from the severest training school in all Eurasia. Where the arid tableland of Arabia is buttressed on the southwestern front by high coast ranges (6000 to 10,500 feet or 2000 to 3200 meters) is Yemen, rich in its soil of disintegrated trap rock, adequately watered by the dash of the southwest monsoons against its towering ridges; but practically the whole country is atilt. Consequently the mountains have been terraced from the base often up to 6000 feet. The country presents the aspect of vast agricultural amphitheaters, in which the narrow paths of ancient paving zigzag up and up through successive zones of production. Here is a wide range of fruits—oranges, lemons, figs, dates, bananas and coffee; then apricots, apples, plums, grapes, quinces, peaches, together with grains of various zonal distribution, such as millet, maize, wheat and barley. The terrace walls are from five to eight feet high, but toward the top of the mountains they often increase to fifteen feet. Though laid without mortar, they are kept in perfect repair. Reservoirs filled with water from the two rainy seasons, supply the irrigation channels.[1271] In the narrow valleys of the Nejd plateau in central Arabia and on the mountain slopes of Oman are found the same irrigated gardens and terraced plantations. This laborious tillage underlay the prosperity of the ancient Sabaean monarchy of Yemen, as it explains the population of 35,000 souls who occupy the modern capital of Sanaa, located at an altitude of 7600 feet (2317 meters).[1272]