42 Reports and Proceedings — Geological Society of London. 



2. " The Eocks of the Cataracts of the Eiver Madeira and the 

 adjoining portions of the Beni and Mamore." By John William 

 Evans, D.Sc, LL.D., F.G.S. 



The crystalline rocks of the cataracts of the River Madeira and 

 the lower waters of its tributaries are part of a ridge with a north- 

 westerly and south-easterly strike, similar to that of the Andes, in 

 the same latitudes. The strike is especially prevalent in Equatorial 

 regions. With the exception of comparatively recent alluvial 

 deposits and a few pebbles of chert, pronounced by Dr. G. J. Hinde 

 to be of marine oi'igin but uncertain date, only crystalline rocks are 

 met with in the falls. They all appear to be igneous, and are mostly 

 massive in character, though some dyke-rocks occur. In places 

 they are typical gneisses, and they are often banded, but in some 

 cases they show no sign of foliation. The prevailing type is acid, 

 with a considerable pi-oportion of alkalies, especially soda ; but some 

 of the rocks are distinctly basic in character. Analyses of several of 

 these rocks, made by Mr. G. S. Blake, are tabulated ; and in one case 

 the chemical analysis is compared with one made from the proportion 

 of minerals washed out from the thin sections. Accounts of the 

 megascopic and microscopic characters of all the rocks encountered, 

 are given. The more acid rocks are usually fine in grain, and are 

 often granulitic in structure. In most cases the quartz seems to 

 have crystallized out before the felspar. The occurrence of andalusite 

 of chiastolitic type and of siliimanite as inclusions in a felspar is 

 referred to, as well as the presence in one rock of an unusual type 

 of allanite. An altered basalt is described, which contains minute 

 concentric structures allied to those of a pyromeride. Above and 

 below the regions of the cataracts is a wide expanse of country 

 covered with alluvium, either of recent or later Tertiary date. 



3. " The Doncaster Earthquake of April 23rd, 1905." By Charles 

 Davison, Sc.D., F.G.S. 



The Doncaster earthquake of 1905 was a twin, with its principal 

 epicentre half a mile north of Bawtry, and the other about four miles 

 east of Crowle and close to the centre of the disturbed area of the 

 Hessle earthquake of April 13th, 1902. The distance between the 

 two epicentres is about 17 miles. The disturbed area contains 

 about 17,000 square miles, including the whole of the counties of 

 Lincoln, Nottingham, Derby, Stafford, Leicester, and Rutland, the 

 greater part of Yorkshire, and portions of Lancashire, Cheshire, 

 Shropshire, Worcestershire, Warwickshire, Northamptonshire, 

 Cambridgeshire, and Norfolk. The originating fault runs from about 

 B. 38° N. to W. 38° S., and appears to be nearly vertical within the 

 south-western focus and inclined to the south-east in the north- 

 eastern focus. The first and stronger movement took place within 

 the south-western focus. A twin earthquake is probably due to 

 the differential growth of a crust-fold along a fault which intersects 

 it transversely, the first movement as a rule being one of rotation 

 of the middle limb, accompanied by an almost simultaneous slip of 

 the two arches, and followed soon afterwards by a shift of the 



