The oldest marine rocks of Persia are of Cambrian age (prob ably Middle). A shallow sea seems to have transgressed over an old levelled surface in Central Persia and in the Gulf region. Near Kerman and at Narghun, 65 miles S.W. of Isfahan, a thin series of trilobite limestones, shales and sandstones has been found. Farther south the Middle Cambrian is developed in a lagoonal facies. Fossiliferous limestones and dolomites, together with sandstones with "salt pseudomorphs," shales and gypsum, have been carried up by intrusive salt masses. The salt is prob ably also of Cambrian age. The fossils include trilobites with Ptychoparia affinities in igneous intrusive rocks of post Cambrian and pre Cenomanian age are present.
Ordovician and Silurian rocks are unknown in Persia, the next marine transgression being of Middle Devonian age. In the Araxes Valley, the Middle Devonian is represented by grey argil laceous limestone containing Calceola sandalina (L.), etc., the Upper by reddish limestones with Spinier verneuili Murch. On the south flank of the Elburz mountains, the Devonian is devel oped in an Old Red Sandstone facies. Middle Devonian lime stones are known near Isfahan. At Narghun a limestone of either Devonian or Lower Carboniferous age is separated from the Cambrian by only zoo ft. of white and pink spotted sand stones. No angular unconformity has been observed.
Carboniferous limestones extend in North Persia from the Araxes valley through the Elburz mountains. Along the Elwand range there is a great development of phyllites or grauwackes. An interbedded limestone has yielded an Orionastraea type of coral, probably Lower Carboniferous. Permo-Carboniferous lime stones with a Punjabian fauna occur at Julfa and in Luristan, in the Kalian Kuh and Kuh-i-Kellar.
The Upper Permian and the Trias are unknown in Persia. A thick series of plant beds perhaps of Rhaetic age is present in the Elburz, followed by marine Lias and Bajocian. East of Lake Urmia, Upper Lias, Callovian and Lower Kimmeridgian fossils have been found. The Upper Jurassic is well developed in north Persia, extending from Armenia eastward to the Hindu Kush. In Central Persia, Lias plant-bearing shales are coal-bearing at several places along the line Hamadan, Isfahan, Kerman. Upper Lias is marine in the Grestener facies. No Jurassic fossils have been found in the Zagros, but a series of red and green radio larian cherts, associated with basic intrusive and extrusive rocks may be of Upper Jurassic or Lower Cretaceous age.
Lower (Neocomian) and Upper Cretaceous rocks are wide spread in the Elburz. In the Zagros mountains, Valanginian and Aptian are known in isolated localities. Upper Cretaceous is well developed and from this time onward to late Tertiary sedimenta tion was continuous in the Mesopotamian—south-west Persian geosyncline. Upper Cretaceous consists of limestones, locally
hippuritic, and fossiliferous marls, often bituminous, which attain a thickness in places of about 3,00o ft. Cretaceous limestones form many of the highest ranges. In Central Persia, Upper Cre taceous is irregularly developed, in places resting with marked unconformity on older rocks.
Eocene is present throughout the greater part of North Persia, but it does not attain any great thickness. In Central Persia it overlies Upper Cretaceous or older rocks unconformably and con sists of limestones and marls with interbedded tuffs and andesitic lava flows. In the Zagros mountains Eocene is present as massive nummulitic limestones or as globigerina marls, up to 2,500 ft. in thickness.
Oligocene is probably represented by tuffs and lavas in North and Central Persia, in Zagros by limestones with Lepidocyclina or Nummulites intermedius-Fichteli, conformably overlying the Eocene.
Miocene unconformably overlies older rocks in North and Central Persia. It consists of limestones, marls and some gypsum. It is not a thick series except in some of the major depressions such as Dasht-i-Kavir. In the Zagros, the Lower Miocene is represented by a massive limestone known as the Asmari lime stone and important as the main reservoir rock of the oil-fields. This is overlain by the Lower Fars gypsum group, then a Middle Miocene marine limestone group, the Middle Fars, followed by a thick series of marls, sands and conglomerates (Upper Fars and Bakhtiaris), extending in age up to Upper Pliocene. In Central Persia, Pliocene is present only in isolated basins. A Pontian bone deposit with Hipparion gracile has been found at Maragha in North Persia, also in Bakhtiari country where it is cemented with bitumen.