ii PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [vol. lxxiv, 



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

 Bendimahi and Bitlis rivers, and thus brought Lake Van into 

 being. 



The history of the Niinrud 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 9000 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 i*ocks are of Miocene (Helvetian-Tortonian) 

 age, occurring north of the JNnnrud Dagh and consisting of lime- 

 stones with corals {Gladocora articulata, Orbicella defrancei, etc.), 

 Lithotliamnion, foraminifera (Lepidocycline Orbiioides, Amplii- 

 stegina, etc.), beds of Pecten {P. urmiensis, etc.) and of oysters 

 (Alectrijoiiia virleti). Nhnrud 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 Anti- 

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

 west to south-east) direction. It also marks the point of inter- 

 section 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. 



3. A presumably long period of inactivity was followed by violent 

 explosions destro} r ing the summit of the cone, and from this crater 

 (smaller than the present one) vast lava-flows of a very fluid basalt 

 (crowded with phenocrysts of labradorite, pale-green augite, and 

 some olivine) flooded the country, filling up the Bitlis and 

 Akhlat valleys, which have since then been eroded a little below 

 their former depth. The Sheikh-Ora crater of basic tuff (now 

 breached by Lake Van) probably belongs to this period. 



4. Further explosions widened the crater, in which a large lake 

 was formed ; while the eastern half of the crater became filled by a 

 succession of outflows of augite-rhyolite, in which numerous blow- 

 holes were drilled, bringing to the surface large blocks of basaltic 

 agglomerate, and also affording sections that show the transition 

 downwards from obsidian, spherulitic obsidian, and spherulitic 

 rhyolite to banded augite-rhyolite (with sanidine and green augite 

 in a rdicropcecilitic ground-mass). 



5. The last eruption was recorded in 1441 by a contemporary 

 Armenian chronicler, and resulted in the extrusion of a very viscous 

 augite-rhyolite along a north-to-south zone of weakness, both inside 



