552 Correspondence — Professor W. W. Watts. 



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

 .explosions destroying 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 and filled 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 showing the transition 

 downwards from obsidian, spherulitic obsidian, and spherulitic 

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

 a micropcecilitic 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 

 the Nimrud crater, where it separated off part of the large lake to 

 form the shallow, so-called "hot lake", and also to the north of 

 Ninirud, where it rose up fissures and in a small crater. 



6. A violent earthquake in 1881, which destroyed the village of 

 Teghurt, at the eastern base of the crater wall, was the last sign of 

 activity ; but earthquakes are still frequent in the Plain of Mush, at 

 the western foot of the Nimrud Dagh, and recent fault-scarps are 

 clearly visible along the borders of this faulted depression. 



The speaker mentioned that lie had presented his model of the 

 crater to the Museum of Practical Geology (Jermyn Street) and the 

 rocks and slides to the British Museum (Natural History), where his 

 fossils from Armenia are already preserved. 1 



A short discussion followed, and the thanks of the Fellows present 

 were accorded to Dr. Oswald for his lecture. 



oozRKESiFonsriDiKiisroE. 



COAL IN THE SILURIAN AT PRESTEIGN. 



Sir, — Mr. Can trill's article in the November number of this 

 Magazine on the boring for coal in Silurian and Longmyndian rocks 

 at Presteign (pp. 481-92) is interesting in throwing light upon 

 one of the most flagrant examples of the ignoring of geological 

 evidence in exploits of this nature. As there must have been some 

 grounds for the impression in the locality that coal existed there, 



1 Lantern-slides of many unpublished photographs and drawings of the 

 Nirnrud crater and its surroundings, a model coloured geologically (scale, 

 1 inch = 1 mile), and a series of rock-specimens and rock-sections were 

 exhibited by Dr. Oswald in illustration of his lecture. A Geological Survey 

 map of the Maclean Umtata district, Cape Province, Sheet 27, scale 

 3-75 miles = 1 inch, 1917 (presented by the Geological Survey of the Union of 

 South Africa), was also exhibited. 



