554 



NATURE 



[Od. 2, 1884 



Karoo Series is traversed with igneous dykes. Limestones and 

 Sandstones (9) with fossils of nearly pure Jurassic, but with some 

 of Cretaceous type, occur unconformably in the Eastern Pro- 

 vince. Their fossil Flora is like that of the Stonnberg Beds. 

 Cretaceous strata (10) are known on the Natal coast : and 

 Tertiary and post-Tertiary deposits (11) form several patches on 

 the east, south, and west coasts. 



The South African Formations 

 11. Tertiary and Post-Tertiary, 100'? 



(Unconformable on several 

 different rocks) 



10. Cretaceous 



9. Jurassic 



Carboniferous ? 



(Unconformable on Carboni- 

 ferous ?) 

 v a (Trigonia Beds ) 



Jf-2 I Wood-bed ( , ? 



c § Saliferous Beds ( ^ 



.-s § Zwartkop Sandstone ) 

 1 3 fe [ Enon Conglomerate, 300' 



(Unconformable on I )i 



and other old rocks in 

 Albany) 

 ( Cave Sandstone, 150' 

 8. Upper Red Beds, 600' 



( Stonnberg Beds, 1000' 

 ( Sandstones and Shales, 5000' 

 7. Lower < 7*. Kimberley or Olive Shales and 

 ( Conglomerates, 2300' 



(Unconformable on Ecca 

 Beds in the south, and on 

 the old Vaal and Kaap 

 series in the north) 

 1 Upper Ecca Beds, 2700' 

 6. Ecca Beds < Dwyka Conglomerate, 500' 



( Lower Ecca Beds, 800' 

 5. Witteberg and Zuurberg Quartzites, 1000' ? 

 4. Table-Mountain Sandstone, 4000' 



(Unconformable on the Old 

 Cape Schists and Slates 

 and on the Bokkeveld Beds 

 3. Bokkeveld Beds, 1 100' 



(Probably unconformable to 

 the Malmesbury Beds) 

 2. Malmesbury Beds, Mica Schists and Slates 

 of the Cape 



(Probable unconformity) 

 1. Namaqualand Schists and Gneiss 



SECTION G— Mechanical Science 

 On the Flow of Water through Tin bin, s, by Arthur Rigg, 

 President of the Society of Engineers, London. — After remark- 

 ing that a strict adherence to the older accepted rules of design 

 never produces thoroughly efficient turbines, and that in the best 

 of such motors these rules are disobeyed, the writer pointed out 

 how little reliable practical information can be obtained from all 

 the voluminous literature relating to turbines. He also stated 

 that the course of a stream flowing through the guides and 

 buckets of a turbine had no appreciable influence upon the duty 

 obtained, so long as one essential condition was observed — 

 namely, that its velocity should be gradually reduced to the least 

 that will carry it clear of the buckets. In comparing screw pro- 

 pellers and turbines, each were shown to possess similarities ; 

 and experiments made by the writer, and published in the 

 Transactions of the Society of Engineers for 186S, were referred 

 to as explanatory of this view of the case. It was further pointed 

 out that there is no such thing as absolute motion, 'for all velocities 

 are relative to something else ; and thus in a turbine we need 

 only concern ourselves with such diminution in velocity as occurs 

 in relation to the earth, and not necessarily with velocities in 

 relation to the moving buckets of a turbine. Impact was con- 

 sidered as a pressure due to the destruction of velocity in a 

 direction perpendicular to a plane surface, while reaction, from 

 a vertical stream, is the natural integration of the horizontal 

 elements of the successive pressures which act vertically in regard 

 to the concave surface upon which the stream is caused to flow. 

 In most theoretical investigations it is assumed that impact and 

 reaction are equal when a current is divided at right angles to its 



original course, and this condition implies that a maximum 

 result should be obtained from screw propellers when their 

 blades stand at 45° to the plane of rotation. But in practice an 

 angle of 42° is found best, and this is so because impact and 

 reaction under the conditions stated are not equal, but bear to 

 each other the proportions of 71 to 62; and these proportions 

 give an inclination of screw-blade of 41° by taking an experiment 

 which corresponds most closely with the conditions of a screw 

 propeller. The resultant due to these proportions is found to be 

 94 '25 units, whereas if impact had been the same as reaction it 

 would have been 10075 units, and this is the total amount that 

 can be aimed for in designing a screw prepellcr, or pure impact 

 turbine, where the stream is merely turned through a right angle 

 from its original course. But if instead of turning the current only 

 go" it is turned through 180 , then impact and a still further 

 reduced reaction both act vertically downwards ; and it is their 

 sum, and not merely their resultant, that constitutes the total 

 pressure obtainable from a jet of water. Taking the standard 

 unit employed in the experiments described, this sum is found to 

 be 126, of which 71 represents impact, and the remaining 55 the 

 effect of a complete reaction. Therefore, in designing a turbine 

 or screw propeller, it would seem desirable to aim at changing the 

 direction of a stream, so far as possible, into one at 1S0 to its 

 original course, for it may be said that carrying out this view has 

 placed the modern scientifically designed turbine in that pre- 

 eminent position it now holds among all hydraulic motors. 



7 'he Severn Tunnel Railway, by T. Clarke Hawk-haw. — This 

 paper described the Severn Tunnel Railway works, begun in 

 1S73, and now approaching completion. The railway is being 

 made to shorten the direct railway route between the South of 

 England and South Wales. It passes under the River Severn 

 about half a mile below the present steam ferry, which connects 

 the South Wales and Bristol and New Passige lines. The river, 

 in estuary, is about i\ miles wide. The length of the line is 

 7 J miles, of which 43 miles are in the tunnel which passes under 

 the Severn. The bed of the river is formed principally of Trias 

 rocks (marls, sandstones, and conglomerates), in nearly hori- 

 zontal strata. These overlie highly inclin d Coal-measure 

 shales and sandstones, which are also exposed in the river bed. 

 The tunnel is made almost wholly in rocks of the Trias and 

 Coal-measure formation, the exception being a little gravel 

 passed through near the English end. The lowest part of the 

 line is below the shoots, the deepest part of the river, where 

 there is a depth of 60 feet of water at the time of low water, and 

 100 feet at the time of high water. Below the shoots, the line 

 is level for 13 chains, rising I in IOO to the English end, and I 

 in 90 to the Welsh end. Below the shoots, there is a thickness 

 of 45 feet of rock (Pennant sandstone) over the brickwork of the 

 tunnel. Under the Salmon Pool there is less cover, only 30 feet 

 of l'i marl. Much water has been met with throughout the 

 works, which have been flooded on several occasions. In 1879 

 the work-, under the Severn were drowned for some months by 

 the eruption of a large land spring into one of the driftways 

 under land on the Welsh side of the river. On another occa- 

 sion a cavil)- was formed from the driftway under the Salmon 

 Pool to the bed of the river, when a hole, 16 feet by 10 feet, was 

 found in the marl. The works were flooded by the water 

 which found an entry through this hole. It was filled with clay, 

 and the tunnel is now finished beneath it. The quantity of 

 w.r. r now being pumped is about 19,000 gallons per minute. 

 Additional pumps have been erected, as the large land spring, 

 which has been penned hack by a brick wall, still remains to be 

 dealt with. When all the pumps are available, the total power 

 will be equal to 41,000 gallons a minute. The tunnel is for a 

 double line of way, and will be lined throughout with vitrified 

 bricks set in Portland cement mortar. It is being made by the 

 .'. istern Railway Company. Sir John Hawkshaw is 

 engineer-in-chief; Mr. C. Richardson, engineer ; and Mr. T. A. 

 Walker, the contractor. 



Section H — Anthropology 

 The first paper read in this Section was that of Prof. Boyd 

 Dawkins, On the Range of the Eskimo in Time ami Space. In 

 his introductory sentences Prof. Pawkins remarked on the 

 importance and interest of his subject. He be_an his inquiry 

 into the condition of the Eskimo by particularising those of 

 Greenland. By the aid of a sketch-map upon the blackboard, 

 he traced the progress of the dwellers on the Arctic shores, fol- 

 low ing them to the continent of Asia. lie noted that in the 



