SECTIONAL TRANSACTIONS.— C. 357 



Wednesday, September 16. 



Mr. V. E. Fuchs. — Lake Rudolf : its formation and history (io.o). 



The Lake Rudolf basin was formed by earth movements that began in 

 the late Oligocene and continued well into Pleistocene times. The chief 

 interest of the area lies in the fact that not only do we see there the northern 

 continuation of the Kenya rift fractures, but also ample evidence of the 

 operation of widespread forces of pressure. 



The initial fracture cut off the northern extension of the Uganda pene- 

 plain, and upon its downthrow side a series of Miocene sediments and 

 volcanics accumulated. These were then asymmetrically folded from east 

 and west towards the axis of the present lake. Accompanied by local 

 thrusting these folds gave rise to the topography of the early Pleistocene 

 lake basin. The deposits formed in it were disturbed by still later move- 

 ments, which, accompanied by vulcanicity, completed the lake basin in its 

 present form. 



To-day the lake does not occupy so large an area as it did because fluctua- 

 ting but progressive desiccation has lowered its level by more than 300 ft. 

 since Acheulian times. Everywhere its high-water mark is defined by lake 

 beaches containing mammalian and molluscan remains together with the 

 stone implements of early man. Modern conditions indicate that the 

 desiccation of the area still continues. 



Mr. W. Campbell Smith. — Igneous rocks from Turkana, Kenya Colony 



(1045)- 



A petrographic study has been made of a large number of rocks collected 

 in the province of Turkana by Mr. Arthur M. Champion. The extrusive 

 rocks include olivine-basalts and basanites from the neighbourhood of the 

 Teleki volcano at the south end of Lake Rudolf, and a series of other lavas 

 comprising soda-rhyolites, pantelleritic trachytes, basalts, phonolites, and 

 nephelinites occupying much of the country west of the lake and as far 

 north as the northern frontier of Kenya Colony. There are some minor 

 intrusions of ijolite, microfoyaite, and solvsbergite. 



Prof. H. H. Swinnerton. — Saline waters and soils of East Lincolnshire 

 ("•IS)- 



The coastal flats, known as the Marshlands of East Lincolnshire, were 

 originally reclaimed from salt marsh. It is generally believed that as the 

 result of exposure to percolating rain water the salt is all washed out of the 

 surface layers of such saline silts. This process is, however, dependent for 

 its efficiency upon an adequate supply of freely flowing river water. Near 

 the south end of the Marshland there is an extensive area where such a supply 

 is not available. Here the soil and the rain water which percolates through 

 it into the drains still hold a high content of salt. 



Reports of Research Committees (11.45). 



