Mount Seir, Sinai and Western Palestine/Chapter 23
CHAPTER XXIII.
EXPLANATION OF THE GEOLOGICAL MAP.
Since this volume contains a Geological Map, it may be expected that I should offer some explanatory observations upon it.
Every good Geological Map ought to explain itself. It ought, in fact, to tell its own story regarding the features of the country it represents, and the rocks and formations of which the region is constructed; and if every person was acquainted with the principles of geology, and had been properly instructed in the plan according to which Geological Maps are prepared, no explanation would be required. With a Geological Map of any district before him, and one also showing the features of hill and dale, mountain and valley, an observer would receive a correct idea of the physical structure of the whole region. He would be able for himself to determine what were the older, or newer, formations: in what way they were disposed one to the other; and, also, be able to form some idea regarding the distribution of land and sea at past periods. Such a map would speak to his mind regarding past physical events as distinctly as a piece of written music, when placed before a musician, conveys to his mind what would be the character of the composition if reproduced on an instrument.
Unfortunately the sublime science of geology has only as yet a limited number of cultivators. Its truths have as yet only been revealed to the favoured few; but the day will doubtless come when the study of geology will be considered as essential to a good education as is the study of geography or history. It is now admitted that geology is the basis of geography; and it cannot be questioned that the physical history of any country has had an important bearing on the history and character of its inhabitants; so that, in order properly to understand the latter, we ought not to neglect the investigation of the former.In no country has this statement a fuller illustration than in the region over which the little Geological Map accompanying this volume extends. The present habits, and much of the past history, of the inhabitants have been moulded on the physical characters of the various parts which are the direct outcome of their geological structure. The mild patient character of the Egyptian cultivator befits the nature of that wide alluvial tract of fertile land which is watered by the Nile, and is one of the most recent tracts reclaimed from the sea.[1] The mountainous tracts of the Sinaitic peninsula, formed of the oldest crystalline rocks of that part of the world, have become the abode of the Bedouin Arab, the hardy child of nature who has adapted himself to a life in keeping with his wild surroundings. The great tableland of the Till, less rugged and inhospitable than the mountainous parts of Sinai and Serbal, supports roving tribes, partly pastoral, and gradually assimilating their habits to the fellahin of Philistia and of Palestine, who cultivate the ground and rear large flocks and herds.
A review of the past history of these regions would probably show a still more intimate connection between the character and habits of the various peoples and the physical features of the country than those even of the present day; but it is not necessary that I should do more than allude to them here, in order to enforce my statement that the connection between their characters and habits may be traced largely to the nature of the country, and this again back to its geological structure. I therefore pass on briefly to explain the meaning of the various colours which have been used in the construction of the map.
It will be seen that the map embraces a large area, extending from the banks of the Nile on the west to the mountains of Edom and Moab on the east, and from the southern extremity of the Sinaitic peninsula on the south, to the mountains of Lebanon on the north. It includes the entire Jordan Valley, and the long continuous depression of the Arabah Valley till it becomes submerged beneath the waters of the Gulf of Akabah.
The oldest rocks occupy the greater portion of the Sinaitic peninsula, as well as the mountains bordering the Gulf of Akabah, and extending northward along the eastern side of the Wâdy el Arabah. They are coloured deep purple and pale pink on the map; and consist of granitic, 
Two isolated masses of the granitic and sandstone formations occur amongst the limestones of the Tîh, and were discovered by Mr. Holland; but details regarding their relations to the newer strata are wanting.[2]
After these ancient rocks had been consolidated they were subjected to a vast amount of erosion, and were worn into very uneven surfaces, over which the more recent formations were spread; first, filling up the hollows with the lower strata, and ultimately covering even the higher elevations as the process of deposition of strata went on.
The oldest of these formations is the red sandstone and conglomerate, which I have called the "Desert Sandstone" formation. It is coloured blue on the map, and forms a narrow strip along the margin of the old crystalline rocks.[3] It is capped by the fossiliferous limestone of the Wâdy Nasb, which shows it to belong to the Carboniferous period—in fact, to be the representative of the Carboniferous Limestone of Europe and the British Isles. It is also found east of the Arabah Valley and amongst the mountains of Moab east of The Ghôr.
This is succeeded by another sandstone formation coloured yellowish brown, and more extensively distributed than the former. It belongs to a much more recent geological period, namely, the Cretaceous; and is the representative of the "Nubian Sandstone" of Roziere, so largely developed in Africa, especially in Nubia and Upper Egypt.
This is succeeded by the Cretaceous and Nummulitic Limestone formations, which occupy the greater portion of the map, forming the great tableland of the Tîh, from its western escarpment to the borders of the Arabah Valley, and stretching northward throughout the hill country of Judea and Samaria into Syria and the Lebanon.
On the east of the Jordan Valley the Cretaceous Limestone forms the tablelands of Edom and Moab; as far north as the Hauran and Jaulan where the limestone passes below great sheets of basaltic lava coloured deep pink. The Cretaceous Limestone is coloured yellow, and represents the Chalk formation of Europe and the British Isles.
The Nummulitic Limestone is represented by a buff colour; but the boundary between the two limestone formations is intentionally indefinite, as it could only be determined with accuracy by a careful and detailed survey and examination of the whole region. Outlying patches of the Nummulitic Limestone occur in Palestine, and are taken from M. Lartet's map; but it is probable that the formation is much more largely represented than is shown on either of those maps. The two formations, although belonging the one to the Secondary, the other to the Tertiary, periods, are very closely connected in Palestine as far as the mineral characters are concerned, though the fossil contents are perhaps altogether different.[4] Both also contain beds and bands of flint or chert.
The Cretaceous Limestone underlies nearly the whole of the Jordan and Arabah Valleys, though concealed by more recent deposits, and is broken off along the line of the great Jordan Valley fault against older formations. This has been explained in a previous page (p. 76), and need not further be insisted on. But it is entirely owing to the presence of this leading line of fracture and displacement, and the subsequent denudation of strata, that this great valley exists, and that the eastern side is so mountainous and characterised by such grand features of hill and dale.
These limestones pass under a newer formation of calcareous sandstone in the direction of the Mediterranean. To this formation I have applied the name of "Calcareous Sandstone of Philistia," as it forms nearly the whole of that country, or at least is its foundation rock. It is probably of Upper Eocene age, and appears to be represented in Egypt by the sandstone formation ("Nicolien Sandstein" of Zittel) with fossil trees found overlying the nummulitic limestone of the Jebel Mokattam, near Cairo. It is coloured deep brown on the map.
The formations next in order approach more nearly those of our own time, and range from the Pliocene period downwards. They consist of raised beaches and sea-beds along the coast, and of lake beds in The Ghôr and Jordan Valley; they are coloured a light shade of green.The volcanic lavas of Northern Palestine and the district bordering the Jordan Valley are coloured deep pink; their geological relations to the other formations have already been pointed out in a previous chapter. The sandy and gravelly tracts are shown by engraved dots.
It is much to be desired that the central portions of the Tîh should be traversed in several directions by competent geologists. From the notes recorded by Mr. Milne and the Rev. F. W. Holland it may be inferred that there is more variety in the stratification of that region than is generally supposed; and that a somewhat detailed reconnaissance would bear interesting results.
- ↑ Coloured deep green on the map.
- ↑ Quarterly Statement, Palestine Exploration Fund, Jan. 1884.
- ↑ A portion of this tract is taken from the Ordnance Survey of Sinai.
- ↑ Dr. Zittel states that although there is no definite line of division between the Cretaceous and Nummulitic formations of the Libyan Desert, the fossils of each formation are entirely different. It is probably the same in Arabia Petræa.