The islands of the Cyclades, Eubœa, Attica, and Laconia, consist for the most part of micaceous schist, combined with and often covered by crystalline granular limestone.[327] The centre and west of Peloponnesus, as well as the country north of the Corinthian gulf from the gulf of Ambrakia to the strait of Eubœa, present a calcareous formation, varying in different localities as to color, consistency, and hardness, but, generally, belonging or approximating to the chalk: it is often very compact, but is distinguished in a marked manner from the crystalline limestone above mentioned. The two loftiest summits in Greece[328] (both, however, lower than Olympus, estimated at nine thousand seven hundred feet) exhibit this formation,—Parnassus, which attains eight thousand feet, and the point of St. Elias in Taygetus, which is not less than seven thousand eight hundred feet. Clay-slate, and conglomerates of sand, lime, and clay, are found in many parts: a close and firm conglomerate of lime composes the Isthmus of Corinth: loose deposits of pebbles, and calcareous breccia, occupy also some portions of the territory. But the most important and essential elements of the Grecian soil, consist of the diluvial and alluvial formations, with which the troughs and basins are filled up, resulting from the decomposition of the older adjoining rocks. In these reside the productive powers of the country, and upon these the grain and vegetables for the subsistence of the people depend. The mountain regions are to a great degree barren, destitute at present of wood or any useful vegetation, though there is reason to believe that they were better wooded in antiquity: in many parts, however, and especially in Ætolia and Akarnania, they afford plenty of timber, and in all parts, pasture for the cattle during summer, at a time when the plains are thoroughly burnt up.[329] For other articles of food, dependence must be had on the valleys, which are occasionally of singular fertility. The low ground of Thessaly, the valley of the Kephisus, and the borders of the lake Kopaïs, in Bœotia, the western portion of Elis, the plains of Stratus on the confines of Akarnania and Ætolia, and those near the river Pamisus in Messenia, both are now, and were in ancient times, remarkable for their abundant produce. [327] For the geological and mineralogical character of Greece, see the survey undertaken by Dr. Fiedler, by orders of the present government of Greece, in 1834 and the following years (Reise durch alle Theile des Königreichs Griechenland in Auftrag der K. G. Regierung in den Jahren 1834 bis 1837, especially vol. ii. pp. 512-530).