File 1450/1919 ‘Mesopotamia & Kurdistan: Geological Reports on’ [‎104v] (223/522)

basal division." There is here a distinct suggestion that the basal
wards at the expense of the OsU-aaverleU stage^ As I have^sa d^P e]ement f of
great unconformity between his 1 ars and Bakhtia , ^ Persian Gulf The historical term used to describe the body of water between the Arabian Peninsula and Iran. In
uncertainty in the correlation of the ^ us ^
the circumstances I would deprecate the use ° f th ® 1 d h also of the term Bakhtiari
for the present m connection with the Fats oi Mesopotam <, ^ , • e . inc i j n sc hemes of
for the later series in the same region. Geology is not a mathemat c< - necessary between
classification—especially in the smaller sub-diyisions-a compiomise is always n^^
chronology" and homotaxis, each of which has claims whith cannot e g , frcsh { {
better position to adjust this compromise in the case m question it is advisable to use es local
n^mesd This has ahvays been found to be the srmplest solution ' j" ads t far S
elsewhere A multiplicity of local names, though burdensome to the mem on, leads tc tar less
confusion than the misuse and subsequent correction of estabhshed terms; it is an ^
drop one or more of the terms when shewn to be unnecessary. Foi the rocks between Mosul
■Kirkuk and Baghdad, all of which can be grouped under the same scheme, i am on y pioposmg
two fresh names for the present. For the gypsum-bearing group, whose base is never seen the
' Bamrin Stage ” of the Fars series would be appropriate. Its uppermost bed is the youngest band
of white gypsum or fossiliferous limestone, and its strata, especially near the top, include short
premature lagoon or river phases. This Hamrm Stage includes, I think the Passage Beds
“Middle Fars” of Halse and Brown as well as their Lower Fars. Id has been called Lower
Fars” in my first nine reports and simply “Fars” in the later ones^ For zone a see Report
No 11 ) of my Red Clay and Sandstone Series, I propose the term Nasaz Zone aftei the range m
which it is so strongly developed. The Red Clay and Sandstone Series is a cumbrous title, for which
the term “ Kurd Series” might be aptly substituted ; further investigation wnl snow to what extent
it is synonymous with the Bakhtiari Series.
The various stages and zones recognizable in this Kurd series have been carefully described in
Report No. 11. The two stages, upper and lower, are always readily distinguishable m a sulhciently
complete succession, but occasionally, through local lateral variation, it is not always easy to
differentiate all the zones, especially “a” and “ b.” My zones a”, b and c —uc., the Lower
Stage of the series—seem to correspond fairly closely with the Upper Fars ot Halse and Brown
Zone “ d”, with the doubtful zone “ e ”, corresponds to their Bakhtiari, up into which they speak of
their Upper Fars as passing. I have not attempted to map the zones in my earlier maps chiefly on
account of the lack of sufficient topographic detail thereon, but they can be readily identified in the
Jabal Hamrin, Jabal Makbul and other localities.
CONGLOMERATES.
It requires experience to be able to distinguish the conglomerates of the Conglomerate Stage
(Nasaz Zone) from Pleistocene or Recent conglomerates and gravels, especially in the neighbourhood
of large rivers. As the pebbles of the younger are precisely similar to, and probably nearly all
derived from, the older conglomerate, there is no distinction in character between them, and
position and dip are the most important criteria. Some of the thinner layers in the Nasaz Zone are
scarcely more than stringers of loose gravel, while the younger Pleistocene deposit may be a very
hard tough conglomerate, such as that on the cliffs above Qalat-al-Bint. In widely isolated
exposures it is sometimes impossible to determine the age of a more or less horizontal conglomerate.
The Tertiary conglomerate exposed in the river cliffs at Tikrit belong to the Nasaz Zone of the Red
Clays and Sandstones ; the normal junction of the latter with the Fars, which it was suggested in
Report No. 1 might be present here, cannot be so therefore. There is little doubt that the cliffs on
the right bank from Tikrit up to Jift and beyond belong to the Nasaz Zone. The conglomerate
seen in the stream-course between Hadraniyah and Qaiyarah and which it was said (Report No. 4)
either belonged to the Conglomerate Stage or to horizons just below, I should now unhesitatingly
refer to that stage (Nasaz Zone) ; in fact the boundary between this stage and the one below
probably coincides fairly closely with the line of this stream, the older stage occurring on the N.E.
side of it.
FORMATION OF HYDROGEN SULPHIDE.
In Report No. 2 it was suggested that the hydrogen sulphide associated with the tarry oil and
bitumen seepages, might be the outcome of the oxidation of petroleum by sulphates, especially by
gypsum, the sulphuric acid radical of the latter being thereby ‘reduced to hydrogen sulphide,
Subsequent experience abundantly supports this view which is not a new one, but has been brought
-forward by others to explain similar phenomena in other countries. Bayerinck and also Saltet have
sfiewn that oxygenated sulphur compounds are reduced by anaerobic bacteria to hydrogen sulphide
in the presence of dead organic matter. It is very unlikely, however, that such organisms can exist
at any appreciable depth below the surface, but experiments by Kharitschoff shew that similar
reduction of sulphates in solution—gypsum and to a still greater extent magnesium sulphate—are
brought about slowly, especially under high pressure and temperature, by hydrocarbons. Hofer
gives equations representing this change :—
Ca S0 4 + CH 4 = CaO + HoS + C0 2 4~ H 2 0
or Ca S0 4 + CH 4 = CaS + C0 2 + 2 H 2 G = Ca Co 3 + H 2 S + H 2 G,
but as Sherburne Rogers remarks, these should be taken merely as type equations, true for the
higher hydrocarbons, since mechone itself is one of the most stable of hydrocarbons and would
probably be the last to undergo any change. In the Mesopotamian seepages oxidation does not
always proceed so far ; the hydrocarbon is not broken up, but unites with the oxygen to form tar or
bitumen. Whether any of the hydrocarbons are completely broken up or not, the total reaction
appears to be exothermic in nature, as the spring in which the hydrogen sulphide is held in solution
is usually warm; the baths of Hammam Ali are an example of this. Rogers formed the opinion that
hydrogen sulphide in the Coalinga and other oil-fields of California was probably produced by the
reduction of sulphate by hydrocarbons. That this is the case in Mesopotamia is borne out by the