362 M. Fergu8son — Notes on Geology of Tanganyika. 



Spurious Earthquakes. 



Shortly after 10 p.m. on July 18, a series of disturbances wa& 

 observed at different places along the south coast of England, 

 between Torquay and Brighton. At first they were supposed to be 

 earthquakes, but they were afterwards traced to the gun-firing during 

 a sham fight which took place at Cherbourg at the hour mentioned 

 in honour of the French President's visit to that town. The 

 evidence for this conclusion is as follows : — (1) The area within 

 which the sounds were heard was a narrow band hardly more than 

 a mile or two wide, following all the windings of the coast, and 

 interrupted in that part of Hampshire shielded from Cherbourg by 

 the higher ground of the Isle of Wight. (2) The disturbances 

 occurred in groups, each of which lasted several minutes. (3) The 

 waves were obviously propagated through the air, for they caused 

 a drumming in the ears, and windows were shaken while floors were 

 still. (4) Lastly, the sounds were recognized as those of heavy 

 guns, and were ascribed to this origin with a confidence which 

 increased with the observer's neighbourhood to Cherbourg. 



VII. — Geological Notes from Tanganyika Northwards. 



By Malcolm Fergusson, Esq. 



("WITH TWO MAPS.) 



THE southern shore of Lake Tanganyika and the country for 

 a distance of 40 miles south of the lake consist of sandstones 

 and conglomerates, dipping north about 10°. These sandstones stretch 

 some little way up the eastern and western shores, and appear to 

 continue away to the south-west. Proceeding further north along 

 the lake shore they get harder, being in places metamorphosed into 

 a pink quartzite. 



In colour the sandstones are reddish or grey, generally very 

 coarse. At the lake they are of enormous thickness, being quite 

 3,000 feet at Kituta, and they surround the southern shore in 

 a precipitous horse-shoe which descends to the water's edge. On 

 the west coast they come to a sudden stop at the Lufu Valley, where 

 there is a break in the range, the plateau descending to the level of 

 the lake into which the Lufu River flows. Here the geology 

 changes, and an intrusive dyke of quartz-felsite comes in, followed 

 by a lava-flow which has every appearance of stratification, and 

 which I mistook for a sedimentary deposit at a distance. It is 

 a rhyolite which has poured down the Sumbu Valley into Cameron 

 Bay, the present appearance being a bank of rhyolite rising from 

 the beach. 



[" Under the microscope the rock has a brecciated appearance, 

 owing to the intermingling of lenticular pink (or in one specimen 

 dark) spherulitic patches with colourless, finer-grained, microfelsitic 

 material showing well-marked flow-structure. A few small pheno- 

 crysts of quartz and altered felspar (mainly oligoclase) are present."] 



