PART III.. =geology.=

=GEOLOGY.=

* * * * *

SECTION IX.—GENERAL AND CLASSIFICATION OF STRATA.

The geology of the area under consideration is almost entirely stratigraphical, the only igneous rocks being more or less local lava flows. The sedimentary rocks of the district have yielded an abundant fauna, both invertebrate and vertebrate; the latter is of unique interest, including as it does a number of highly interesting animal types quite new to science. An extended examination in the field, and comparisons with the stratigraphical succession in other parts of Egypt, checked by the determinations of the fossil molluscan fauna, make it possible to form a very fair estimate of the approximate age of the different rock-stages, although this may necessarily be subject to modification when the specific determinations of the entire collection of organic remains have been completed, and the development of vertebrate life has been correlated and compared with that in other parts of the world.

The depression is cut out in a great series of sedimentary rocks of Middle Eocene, Upper Eocene, and Oligocene age, and one of the features of the stratigraphy of the region is the constancy of many beds over wide areas. The dip of the beds throughout the area is nearly due north and at a very low angle, averaging 2° or 3°, but varying from 1° to 5°; this low dip is very constantly maintained except when locally affected by small faults. The structural geology and tectonics have already been discussed at some length in the previous sections.

The oldest beds found in the depression are the clays, marls, and limestones with Nummulites gizehensis, of Middle Eocene age. These are succeeded by a group of white marly limestones and gypseous clays, which largely underlie the cultivated alluvium of the Fayûm. They are followed by a series consisting of clays, sandstones, and calcareous grits, some beds of which are characterized by the abundance of small nummulites and Operculina. The latter series is followed by the uppermost truly marine Eocene beds, a group of alternating clays, sandstones and limestones, the “Qasr el Sagha Series” (or Carolia beds), characterized by an abundant invertebrate and vertebrate fauna, and equivalent to the Upper Mokattam beds of Cairo.

Above the Qasr el Sagha series, and well marked off from them both lithologically and palæontologically, is found a great thickness of variegated sands, sandstones, clays and marls, the “Fluvio-marine Series” (Jebel el Qatrani beds), divided near the summit by one or more thick intercalated lava sheets, the latter forming a convenient junction line. This series of variegated beds is of Upper Eocene—Lower Oligocene age.

No Miocene strata have been recognized within the area, but further north, as at Mogara, Lower Miocene deposits occur; and it is probable that there is a continuous series of lithologically similar beds from the summit of the Fayûm escarpments (Lower Oligocene) to the Mogara Miocene.

The Pliocene is probably represented by the great terraces of gravel—raised beaches—which are such a marked feature in the geology of the district. Fossiliferous Pliocene deposits have also been recorded from the south part of the area by Schweinfurth.

Pleistocene and Recent are abundantly represented by lacustrine clays, both ancient and modern, alluvial land and blown sand, the formation of which deposits is continuing at the present time.

The following table will show the sequence of strata and the classification adopted in the present memoir:—

TABLE SHOWING SUCCESSION AND CLASSIFICATION OF STRATA IN THE FAYUM.

-----------+---------+--------+-----------+--------------------------- | | |Approximate| | | | average | | | | thickness | | | | in metres,| | | | north part| | | | of Fayum. | | | +-----------| | | | | Alluvial soil, clays, | | | | sands, etc. RECENT | | | | AND | | | | Blown sand. PLEISTOCENE| | | | | | | | Lacustrine clays, | | | | extending to about 23 | | | | metres above sea-level. -----------+---------+--------+-----------+--------------------------- | | | | Gravel Terraces (? | | | | Pleistocene). | | | | (MIDDLE?) | | | | Shell-borings on rock PLIOCENE | | | | surfaces. | | | | | | | 50 | Fossiliferous deposits of | | | | Sidmant. -----------+---------+--------+-----------+--------------------------- | | | |Fluvio-marine Series | | | |(Jebel el Qatrani beds). | | | | LOWER | | | 30 | Sandstones and OLIGOCENE |TONGRIAN | | | sandstone-grits with | | | | silicified trees and | | | | | | | | Basalt sheets, | | | | interbedded and | | | | contemporaneous. -----------+---------+--------+-----------+- - - - - - - - - - - - - - | | | | Variegated sands, | | | | sandstones, clays and | | | | marls, with | | | | limestone-grits and thin | | | | bands of limestone. The | | | | upper beds contain Unio | | | | sp., Lanistes | | | | bartonianus, Blanck., | | | | Turritella pharaonica, | | | | Cossm., Potamides | | | | scalaroides, Desh., P. | | | | tristriatus, Lam., | | | | Pleurotoma ingens, | | | | May.-Eym. In the lower | | | | beds are large numbers of | | | | silicified trees | | | | associated with | | | | vertebrate remains | | | | including Arsinoitherium | | | | Zitteli, Beadn., A. | | | | Andrewsii, Lankester, UPPER | | | | Palæomastodon EOCENE |BARTONIAN| | 250 | Beadnelli, Andr., P. | | | | minor, Andr., | | | | Mœritherium Lyonsi, | | | | Andr., M. trigodon, | | | | Andr., Megalohyrax | | | | eocænus, Andr., M. | | | | minor Andr., | | | | Saghatherium antiquum, | | | | Andr. and Beadn., S. | | | | minus, Andr. and Beadn., | | | | S. magnum, Andr., | | | | Ancodus Gorringei, | | | | Andr. and Beadn., | | | | Geniohyus mirus, Andr., | | | | G. fayumensis, Andr., | | | | G. major, Andr., | | | | Phiomia serridens, | | | | Andr. and Beadn., | | | | Pterodon africanus, | | | | Andr., P. macrognathus, | | | | Andr., Eremopezus | | | | libycus, Andr., Testudo | | | | Ammon, Andr., and | | | | frequent crocodilian and | | | | chelonian remains. -----------+---------+--------+-----------+--------------------------- | | | |Qasr el Sagha Series | | | |(Carolia beds). | | | | | | | | Alternating limestones, | | | | marls, clays and | | | | sandstones with Qerunia | | | | (Hydractinia) | | | | cornuta, May.-Eym., | | | | Astrohelia similis, | | | | Felix., Echinolampas | | | | Crameri, Loriol., | | | | Ostrea Reili, Fraas, | | | | Ostrea elegans, Desh., | | | | Alectryonia Clot-Beyi, | | | | Bellardi, Exogyra | | | | Fraasi, May.-Eym., | | | | Carolia placunoides, | | | | Cantr., Cardita | | | | fajumensis, Oppenh., | | UPPER | | Macrosolen Hollowaysi, | |MOKATTAM| 155 | Sowerby, Turritella | | | | pharaonica, Cossm., T. | | | | carinifera, Desh., | | | | Mesalia fasciata, Lam., | | | | Rimella rimosa, Sol. | | | | The vertebrate remains | | | | include Mœritherium | | | | Lyonsi, Andr., M. | | | | gracilis, Andr., | | | | Barytherium grave, | | | | Andr., Eosiren libyca, | | | | Andr., Zeuglodon | | | | Osiris, Dames, | | | | Gigantophis Garstini, | | | | Andr., Pterosphenus | | | | Schweinfurthi, Andr., | | | | Psephophorus eocænus, | | | | Andr., Thallassochelys | | | | libyca, Andr., | | | | Podocnemis antiqua, | | | | Andr., P. Stromeri, v. | | | | Rein., Stereogenys | | | | Cromeri, Andr., S. | | | | podocnemioides, v. | | | | Rein., Tomistoma | | | | africanum, Andr., with | | | | siluroids and Propristis MIDDLE | | | | Schweinfurthi, Dames. EOCENE |PARISIAN |--------+-----------+--------------------------- | | | |Birket el Qurûn Series | | | |(Operculina-Nummulite | | | |beds). | | | | | | | | Sandstones and clays, | | | | with sandy limestones, | | | | and one or more well | | | | marked concretionary | | | | sandstones weathering | | | | into large globular | | | | masses. | | | | | | | | Nummulites Fraasi, de | | | | la Harpe, N. Beaumonti, | | | 50 | Operculina discoidea, | | | | Schwag., Qerunia | | | | cornuta, May.-Eym., | | | | Plicatula polymorpha, | | | | Bell., Pectunculus | | | | pseudopulvinatus, Orb., | | | | Cardita Viquesneli, | | | | d’Arch., Cardium | | | | Schweinfurthi, | | | | May.-Eym., Venus | | | | plicatella, May.-Eym., | | | | Macrosolen Hollowaysi, | | | | Sow., Lucina pharaonis, | | | | Bell., Tellina | | | | scalaroides, Lam., | | | | Clavellithes longævus, | | | | Sol., Voluta arabica, | | | | May.-Eym., Turritella | | | | pharaonica, Cossm., T. | | | | carinifera, Desh., with | | | | Zeuglodon Osiris, | | | | Dames, and Z. Isis, | | | | Beadn. | | LOWER +-----------+--------------------------- | |MOKATTAM| |Ravine Beds. | | | | | | | 70 | White marls and marly | | | | limestones with gypseous | | | | clays; Nucularia sp. | | | | Leda sp., Corbula | | | | aff. pixidicula, Desh., | | | | Lucina sp. (? | | | | pharaonis), Tellina | | | | tenuistriata, Desh., | | | | Zeuglodon Isis, Beadn., | | | | and scales and teeth of | | | | fish. | | |-----------+--------------------------- | | | |Wadi Rayan Series | | | |(Nummulites gizehensis | | | |beds). | | | | | | | 130 | Limestones, marls, clays, | | | | etc., with Nummulites | | | | gizehensis, Ehrbg., N. | | | | curvispira, Carolia | | | | placunoides, Cantr. -----------+---------+--------+-----------+---------------------------