File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎85v] (185/522)

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Alternating with the gypsum and limestone bands are beds of sandy clay, sometimes gypseous
and marly, frequently permeated with thin laminae of translucent selenite derived from the gypsum.
This clay is typically of a light greenish or brownish pink colour, and is sometimes—as for instance
half-way between Fathah and Ain Nukhailah—stained a conspicuous red with ( xide of iron. Both
gypsum and gypseous clay in the neighbourhood of oil seepages contain yellow sulphur, and give forth
a strong odour of hydrogen sulphide. It is a matter for consideration whether the sulphur and
hydrogen sulphide have not originated by the reduction of sulphates by crude oil which has as a
result been oxidised to tar and bitumen. Small pockets of red oxide of iron are sometimes to be
■seen in the gypseous clays.
Since neither range is penetrated very deeply by streams, not more than about 600 feet of the
Lower Pars are exposed in the Jabal-Hamrin and between 600 and 700 feet in the Jabal-Makhul.
Red Clay and Sandstone Series (? Bakhtiari). The Lower Pars is succeeded by thick
feeds of somewhat sandy soft red clay containing near the base two or three isolated layers, an inch
or two thick, of selenite derived from the gypsum below ; these follow the digs of the clays. One
■characteristic band occurring within the first 50 feet is that of a light bluish unfossiliferous marl, less
than a foot thick ; this was observed in widely separated areas, for instance at Ain Khalid (near Ain
Nukhailah) and near Qalat-al-Bint some 16 miles N.N.W. of Fathah. Bands of red brown sandstone,
at first very thin and argillaceous, soon appear, and increase in size and purity further up in the series
until they predominate over the clays in massive current-bedded sand-rock of medium to coarse
texture. Near Ain Nukhailah incipient root-like concretions produced a fretted weathered surface
on this sand-rock. Thin gravel or conglomerate bands next appear and one of these forms the line
of low mound-like hills which stretches practically continuous from the N. of Ain Nukhailah to the
neighbourhood of the river, where it swings round to the N.W. These mounds have evidently been
submerged beneath the alluvial waters and are loosely strewn with gravel which largely conceals the
Tertiary beds beneath. This is the highest Tertiary horizon properly exposed, the Alluvium
sweeping up its dip-slope. The pebbles in the conglomerates are mostly of siliceous sandstone,
chert and white quartz ; they are the same as those in the Pleistocene conglomerate and the recent
gravels, which have already been described. The whole of this series seems to have offered a
surprisingly feeble resistance to erosion, and is nearly always largely mashed by alluvium, outcrops
of sandstone cropping out here and there in the deeper stream-courses.
There is occasionally a decrease in dip passing from the Lower Pars to the red clays, but usually
there is no change in dip ; the highest bed of the Lower Pars, a band of white gypsum, is
succeeded by a bed of red clay containing one or two thin layers of selenite and the thin band of
bluish marl, and there is the appearance of conformity. I say “appearance/' because, although my
■cursory survey with small scale maps was unable to shew that any extensive erosion of the Lower
Pars took place before the deposition of the younger series, the change from one to the other is
sudden, sharp and distinct ; above the boundary no sedimentary gypsum bands nor fossiliferous
limestone occur, the only points in common being a slight resemblance of the clays. It is a line
along which one at once suspects unconformity, and I feel convinced that such will be found—perhaps
very marked locally—in other localities, and very probably in the area under description when maps
of a larger scale are available.
This red clay and sandstone series corresponds to the Upper Pars of James Halse and Brown,
but I prefer to give it no definite assignation provisionally until more of it has been seen for the
following reasons. Dr. Pilgrim split up Loftus Gypseous Group into the Pars and Bakhtiari,
chiefly, I take it, because he found this group to consist of a lower marine and an upper fluviatile
deposit. The Upper Pars of Dr. Pilgrim is a highly fossiliferous marine deposit with a rich fauna.
The red clay and sandstone series of the Jabal-Hamrin is unfossiliferous and has every appearance
of a fluviatile deposit, and I cannot see why it should not be classed as homotaxially equivalent to
Dr. Pilgrim’s Bakhtiari sandstone series, which is described, moreover, as being characterised by
red clays at its base and conglomerates further up.
The best exposures of the beds is N. of Ain Nukhailah where over 3,000 feet can be studied.
They are also well seen, though in less thickness, between the Jabal-Makhul and the Jabal-Khanuqah ;
the conglomeratic stage is not present here. When not protected by sufficiently thick alluvial
deposits, this series produces the most broken kind of ground which is as bewildering to the eye as
wearisome to the feet.
Pleistocene. A high-lying conglomerate occurring in the vicinity of the river, at heights
varying from about 300 to 500 feet above the Mesopotamian plain, is probably referable to the
Pleistocene. It is seen capping the end of the Jabal-Hamrin above Fathah and a small patch occurs
on the other side of the river on the Jabal-Makhul. On the hills above the Humr Plain S.E. of
Qalat-al-Bint it forms a distinct plateau in places. It is not seen in the higher parts of the Hamrin
and Makhul ranges. It lies unconformably upon the Lower Pars and it is doubtful whether any
perceptible dip is demonstrable. It is sometimes a tough conglomerate seveial feet thick but is
usually soft enough to disintegrate under the hammer and in many cases is represented only by a
loose gravel strewn over the tops of the hills ; in the latter case it is only its altitude which
distinguishes it from the recent gravel of the Mesopotamian Alluvium. Its pebbles consist of the
same siliceous rocks as those forming the Tertiary conglomerates already described, and frequently
attain 9—10 inches across, though the average size is nearer 2—3 inches. This conglomerate,
derived doubtless from the conglomerates of the Red Clay and Sandstone series, is evidently a gravel
deposit of the Pleistocene ancestor of the present Tigris, which must have flowed over a large part
of the continuation of the Jabal-Khanuqah overlooking the Humr Plain.
Recent. The Mesopotamian Alluvium has been referred to in an earlier report. It has inter-
bedded pockets of gravel, to be seen on both banks of the river at Fathah, at the N.W. corner of
the Humr Plain and elsewhere. Its pebbles, derived from the Pleistocene and Tertiary conglom
erates, consist of the same siliceous sandstone, chert, quartz, igneous greenstone and rarer pieces
of grey fimestone : in addition fragments of a blue-black pumice were observed between Fathah and
Nukhailah. The Mesopotamian Alluvium covers nearly all the Red Clay and Sandstone series,
which is not always clearly exposed in consequence ; the very broken ground between the D/ 3 . 3 -*
Makhul and the hills above Humr, for instance, really forms part of an alluvial plain through which