A principal cause of this clearness and pellucidness is the great prevalence of the north wind,[153] which brings with it few or no vapours, but gathers together the clouds in heaps and rolls them from the land towards the Mediterranean. The reason why this wind so often prevails may be discovered in the geographical configuration of the country, which is not, like Italy, divided from the rest of the continent by a range of Alps that might have screened it from the colder blasts, but lies open like an elevated threshing-floor, to be purged and winnowed on all sides by the winds, which in many parts are so violent that no tree can attain to any great height, while the stunted woods throw all their branches in one direction, and the vines and other climbing shrubs are laid prostrate along the rocks. These winds, however, prevail not constantly, but the southern and western breezes, blowing at intervals, bring along with them the warm atmosphere of Syria or Egypt, or the cooling freshness of the ocean. Another cause, which greatly tends to promote the purity of the air, is the lightness, friability, and dryness of the soil, which, distributed for the most part in thin layers over ledges of rocks, permits no stagnation of moisture, but enables the rain that falls to trickle through, collect in rills and brooks, and find its way rapidly to the sea. The plains and irregular valleys, which form an exception to this rule, are not numerous enough, or of sufficient magnitude to affect the general proposition. There appear, moreover, to be many peculiar properties and virtues in the soil itself, causing all fruits transplanted thither to attain to speedy ripeness and superior flavour, while odoriferous plants and flowers, as the jasmine, the wild thyme, and the rose exhale sweeter and more delicious fragrance. This is more particularly the case in Attica, which accordingly produced in antiquity, where due care was bestowed on gardening and agriculture, the finest fruits and sweetest honey in the world.[154] Footnote 153: This wind, wherever it prevails, increases the appetite; and the Greeks were a hearty-eating people.—Aristot. Probl. xxvi. 45. The wind Ornithias was often so cold as to strike birds dead on the wing. Schol. Aristoph. Ach. 842. Footnote 154: Aristot. Probl. xx. 20. The black myrtle, which is much larger than the white, grew wild about the hills. (xx. 36.) The southern breezes were considered highly salutary to the plants of the Thriasian plain. (xxvi. 18.)