Reports & Proceedings — Geological Society of London. 551 



The Ninirud volcano, one of the largest volcanic craters in the 

 world, is situated on the western shore of Lake Yan, and was 

 surveyed and investigated geologically for the first time by the 

 speaker in 1898. The western half of the crater is occupied by 

 a deep lake of fresh water, while the eastern half is composed of 

 recent augite-rhyolites, partly cloaked in white volcanic ash. The 

 crater wall is highest on the north (9,903 feet), rising in abrupt 

 precipices over 2,000 feet above the lake (7,653 feet). The southern 

 wall is also precipitous, but only reaches the height of 9,434 feet 

 (the south-eastern part). A large slice of the crater wall has slipped 

 down on the south-west, so as to form a narrow shelf, 800 feet above 

 the lake. The crater is nearly circular, 8,405 yards from west-south- 

 west to east-north-east, while the transverse axis is 7,905 yards. 

 The lowest points lie on the long axis, reaching only 8,139 feet on 

 the western and 8,148 feet on the eastern rim. 



The crater wall has an external slope of 33° on the south and east, 

 where it consists exclusively of overlapping lenticular flows of augite- 

 rhyolite and obsidian. On the south-west, west, north-west, and 

 north these are capped by thin sheets of cindery basalt which must 

 have possessed great fluidity, extending for many miles to form wide 

 plains of gentle slope and great fertility down to Lake Yan on the 

 east and into the Plain of Mush on the west. These basalt-flows 

 dammed up the north-east to south-west valley between the 

 Bendimahi and Bitlis Rivers, and thus brought Lake Yan into being. 



The history of the Nimrud volcano may be summarized as follows 

 from the speaker's observations : — 



1. Its forerunner was the Kerkur Dagh on its southern flank — 

 a denuded mass of grey augite-trachyte, rising to 9,000 feet, and 

 crowned by many peaks. It was probably erupted in the Pliocene 

 Period, subsequently to the folding of the Armenian area, in which 

 the latest folded rocks are of Miocene (Helvetian-Tortonian) age, 

 occurring north of the Nirnrud Dagh and consisting of limestones 

 with corals ( Cladocora articulata, Orbicella defrancei, etc.), Litho- 

 thamnion, Poraminifera (Lepidocycline Orlitoides, Amphistegina, etc.), 

 beds of Pecten (P. urmiensis, etc.) and of oysters (Alectryonia virleti). 

 Mmrud and the other numerous volcanoes of Armenia came into 

 existence at a period when the sedimentary rocks could no longer be 

 folded, but were fractured along definite lines, and Nimrud is 

 situated on the great fracture transverse to the Armenian folds at 

 the apex of their bending round from the Antitauric (west-south- 

 west to east-north-east) to the Persian (north-west to south-east) 

 direction, and it also marks the point of intersection of this fracture 

 with a great north-east to north-west fracture (Caucasian direction), 

 which delimits on the south Lake Van and the faulted depression of 

 the Plain of Mush, abruptly cutting off the Tauric horst of pre- 

 Devonian marbles and mica-schists. 



2. Numerous flows of augite-rhyolite built up the vast cone of the 

 Nimrud Dagh, and the increasing pressure on the central vent 

 became relieved by extrusions of augite-trachyte along radial 

 fissures, forming the present promontories of Kizvag, Zighag, and 

 Karmuch. 



