GEOLOGY OF PALESTINE [ISBE]
GEOLOGY OF PALESTINE
- je-ol'-o-ji, The geology of Palestine cannot be discussed intelligently without taking into consideration the surrounding regions. The accompanying map shows, with considerable freedom, the distribution of the superficial strata of Syria, Palestine and Sinai, with parts of Asia Minor, Arabia and Egypt. (Data for this map were obtained from the "Geological Map of Egypt" (1:1,000,000) and from the "Carte geologique internationale de l'Europe" (1:1,500,000).) It will be noted that Crystalline, or Archean, rocks (A) occupy extensive areas in Asia Minor, and that they are found in the South in Sinai, Western Arabia, and Eastern and Southern Egypt. Relatively small areas of Paleozoic rocks (P) adjoin the Crystalline rocks in Sinai and Arabia and East of Caesarea in Asia Minor. A notable area of Paleozoic occurs Southeast of the Dead Sea. This is also adjacent to Crystalline rocks, which could not be indicated on the map on account of their slight superficial extent. Bordering either the Crystalline or the Paleozoic rocks in Egypt, Sinai and Arabia are large areas of Nubian Sandstone (N). The Nubian Sandstone in turn is generally bounded by Upper Cretaceous limestone (C), and the last by Tertiary deposits (T). The Quaternary, or Recent, deposits (R) and also the Eruptive rocks (E) sustain no constant relations to any particular ones of the other formations. The Quaternary follows the great rivers and the seacoasts. The Eruptive rocks usually overlie the others. They occupy extensive areas in Asia Minor, Syria and Arabia.
If we concentrate our attention upon the Crystalline, Cretaceous, and Tertiary, which are the most extensive formations, we find that the Crystalline rocks are abundant in the South and in the North, that the Cretaceous are most widely spread in Palestine and Southern Syria, and the Tertiary in Northern Syria and Egypt. We may believe that the Crystalline areas of the North and South have been land since the end of the Archean age, and that what are now Syria, Palestine and most of Egypt remained sea for a long time afterward. The Paleozoic areas were lifted above the sea and added to the northern and southern land areas during or at the end of the Paleozoic era. The regions in which we find Nubian Sandstone or Upper Cretaceous limestone became land by the end of the Mesozoic era. Finally the Tertiary areas were lifted out of the sea. During the Quaternary period the Nile and the rivers of Mesopotamia have added large areas to the land surface.
1. Crystalline Rocks (A):
The Crystalline rocks consist mainly of granite and crystalline schists, frequently interrupted with dikes of porphyry, diorite and other eruptives. It will be seen by the map that the Crystalline rocks are nowhere adjacent to the Mediterranean, but that they touch the Nile at Acwan, where the river in pouring over these rocks makes the First Cataract, or rather did before the construction of the great dam. Granite quarried at Acwan could be loaded on boats and conveyed to any city on the shores of the Mediterranean, and it is the granite of Acwan of which are composed not only many of the monuments of Egypt, but also the pillars which adorned many temples in Syria and Palestine.
2. Paleozoic Rocks (P):
The Paleozoic rocks of Sinai and Arabia are of Carboniferous age, but do not include any beds of coal. Those East of Caesarea are Devonian. Those Southeast of the Dead Sea are the oldest of all, being of Cambrian age.
3. Triassic and Jurassic Rocks (Jahwist):
Several formations which are well developed in the British Islands, are not found in Palestine, but a small Triassic area is found near the Gulf of Alexandretta, while Jurassic strata are found in the region of Hermon and in Lebanon and Anti-Lebanon. The small scale of the accompanying map makes it impossible to represent accurately the extent of these rocks.
4. Nubian Sandstone (N):
This name was given by Russegger, who in the middle of the 19th century followed and studied this formation from the Sudan to Syria. Wherever the Nubian Sandstone is found in contact with the Upper Cretaceous limestone it underlies the latter conformably. In Lebanon, Anti-Lebanon and Hermon (but not farther South) it is conformably underlaid by Jurassic limestone. It follows, therefore, that its upper strata (the only ones found in the North) must be of Lower or Middle Cretaceous age. In the South, however, the Jurassic limestone is entirely absent. In Western Sinai the Nubian Sandstone rests conformably on Carboniferous limestone, and by the Dead Sea on Cambrian limestone, while at Petra and at many other places it rests unconformably on Crystalline rocks. While the consideration of the age of the Nubian Sandstone presents no difficulty in Lebanon, Anti-Lebanon and Hermon, it is a very different matter in Western Sinai, and by the Dead Sea. Sandstone is generally supposed to be formed more rapidly than most other rocks. It is, therefore, rather staggering to try to conceive of even the 2,000 ft. of sandstone at the Southeast end of the Dead Sea as having been in process of formation from the Cambrian to the Cretaceous. The Nubian Sandstone is commonly brown or reddish, but in places shows great variety of color. The temples and tombs of Petra were all carved in this rock. It is in places very friable, and in others compact and hard. The sands of the Arabian deserts have been in the main derived from it, being carried by the prevailing west winds. Where it is covered by a sheet of eruptive rock (charrah), it is protected from erosion, with the result that the land to the East is not converted into a sandy desert (Hogarth, Penetration of Arabia). It frequently includes strata of clay and shale and thin seams of coal or lignite, and must have been deposited in seas which were at the time relatively shallow.
5. Upper Cretaceous Limestone (C):
This is the principal rock of Palestine, Lebanon, and Anti-Lebanon. Many of its strata are very fossiliferous, and no doubt exists as to its age. It furnishes the best of building stone and is a source of lime. The soils formed from it are fertile, and the mountain sides have been terraced by the patient labor of centuries.
6. Tertiary Rocks (T):
A notable Tertiary fossil is the Nummulite, which occurs in abundance in the rock of the pyramids of Gizeh and in other places. Relatively small masses of Tertiary strata (not shown on the map) are found on the coast at the mouths of the principal streams of Lebanon, showing that while the mass of Lebanon had risen from the sea by the beginning of the Tertiary, the elevation was not complete. The principal river courses had, however, already been formed, and the streams were already carrying into the sea the scourings of the rocks of early Lebanon, which were being laid down to form these Tertiary strata.
7. Quaternary and Recent Strata (R):
These consist mainly of the superficial deposits of the Nile, the Euphrates and other large streams. At various points along the coast of Syria and Palestine are extensive sand dunes. Frequently under the loose sand, or exposed, is found a sandstone which instead of being entirely siliceous, like most sandstones, is partly calcareous, containing from 15 to 25 per cent of calcium-carbonate. This is probably an aeolian formation, i.e. consolidated under the influence of the atmosphere, and not formed under the sea, like most stratified rocks. It is easily worked and is much used for building.
It may be gathered from the foregoing statements that the rocks of Palestine are mainly Cretaceous. The Jurassic limestone, which in Lebanon and Anti-Lebanon underlies the Nubian Sandstone, is absent in Palestine, but, at least in Eastern Palestine, as in Lebanon, we find the Upper Cretaceous limestone to be underlaid by the Nubian Sandstone. A striking feature of the geology of Palestine is the Jordan valley fault. At some time, probably at the beginning of the Tertiary period, when Lebanon, Anti-Lebanon, and the Judean hills were being lifted out of the sea, the earth's crust was rent for at least several hundred miles along a line nearly North and South, or more exactly from a little West of South to a little East of North. This line runs through the Gulf of `Aqabah, the Wadi-`Arabah, the Dead Sea, the Jordan valley, the Sea of Tiberias, the Chuleh, and the valley between Hermon and Anti-Lebanon on the one hand and Lebanon on the other. The resulting disturbance of the strata is most evident in the region of the Dead Sea. There is no evidence that the two walls of the fissure separated from one another, but the East wall slipped up and the West wall down for perhaps 2,000 ft, so that on the East shore of the Dead Sea and in the valleys entering the Jordan, Dead Sea, and `Arabah from the East, the Nubian Sandstone is exposed, underlying the Upper Cretaceous limestone, while on the West side, even down to the level of the Dead Sea, 1,290 ft. below the Mediterranean, the Nubian Sandstone is nowhere visible, although it may be presumed to exist there also below the upper limestone. (See the accompanying ideal section, after Lartet, through Judea, the Dead Sea and Moab.) The great fault and the subsidiary faults which accompany it occasioned the outpourings of igneous rock which are abundant along the line of the fault. The numerous hot springs (e.g. Tiberins, Wadi-Yarmuk, Wadi-Zarqa-Ma`in (Callirrhoe), Wadi-ul-Chisa) may be due to subterranean streams of water coming in contact with deeply buried and still heated masses of igneous rock.
Alfred Ely Day