July 6, 1882] 



XATURE 



229 



in his decision as to the exact place by the direction of 

 their upper portions. 



I find, however, on trial that another cause of confusion 

 lies in the difficulty of watching closely both the fore and 

 the hind halves of the animal simultaneously. The eye 

 wanders from one to the other and seizes the most cha- 

 racteristic attitudes of each, and combines them into a 

 hybrid monster. 



The accompanying composites, Figs. 1 and 2, each 

 •"rom four successive attitudes, will explain the process ; it 

 certainly tends to go on in my mind, and probably does 



so in that of others. The first composite shows the hind 

 legs distinctly ; the second shows the fore legs distinctly ; 

 and if duplicates of the first and second woodcuts are 

 each divided in two halves and the best defined half of 

 each are united (in a way that might have occurred to 

 Baron Munchausen if a second rider's horse had suffered 

 as his own, and there had been a mistake in piecing them), 

 a result, Fig. 3, is produced that shows a very fair 

 correspondence with a not uncommon representation in 

 sculpture. Francis Galton 



THE CHANNEL TUNNEL 

 AT the meeting of the Paris Academy of June 26, M. 

 - r *- Daubre'e read a note on the geological conditions of 

 the Channel tunnel. The works connected with the 

 tunnel comprise three phases :— (1) Scientific researches; 

 (2) preparatory works ; (3) execution of the tunnel itself. 

 The first phase was devoted to purely geological investi- 

 gation, in the form of minute exploration of the French 

 and English coasts, exact and detailed investigation of 

 the sea-bottom in the Strait, borings made on terra 

 jirma which verified the nature, thickness, and inclination 

 of the strata, and gave an approximate idea of the hydro- 

 logical condition. Since 1879 the second phase has been 

 entered on by verifying the previous scientific data, and 

 preparing for the execution of the tunnel itself, experi- 

 menting in small galleries with machines and too', capable 

 of being ultimately used in a work of exceptional import- 

 ance. On the French coast, the geological investigation 

 established a slight bulging of the beds at the'place 

 known as the Qftenocs. On account of this bulging the 

 inclination of the strata, which, in the strait is towards the 

 north-north-east, is found, along the cliffs of Blanc Xez, 

 turned towards the south-east, and the slope which, 

 according to the first orientation, in the neighbourhood 

 of the Quenocs, is about 0-05 m. per metre, is found, in 

 the second, to be nearly 0-09 m. It is important then, to 

 find in what conditions this bulging may modify the 

 physical conditions of the banks forming the base of the 

 Rouen chalk. For this purpose the French Association 

 had dug, near Sangatte, two shafts of a depth of 86 m., 



which met the gault at 59 m. below the hydrographic 

 zero, adopted in the maps in which the geological explo- 

 rations of 1875-6 are recorded. The digging of these 

 shafts, one of them 5 40 m. in diameter, showed that all 

 the white chalk and the upper part of the Rouen chalk 

 are water-bearing. These strata had thus to be aban- 

 doned. 



On the other hand, the base of the Rouen chalk allowed 

 only a very small portion of water to pass. There, then, 

 the tunnel should be pierced, as the stratum appeared to 

 proceed without interruption from France to England. 

 The water penetrating the works is fresh, and of good 

 quality ; at the upper part only some slightly salt veins 

 were found. Nevertheless, the communication of the 

 water-bearing strata with the sea is proved by the oscilla- 

 tion of the water-level in the shafts according to the tide, 

 and by the invariable increase at high water. M. Daubre'e 

 then refers to further galleries dug on the French and 

 on the English sides, and excavations made with the 

 machines of Col. Beaumont and Mr. Brunton On the 

 Dover side, the chalk, which on the French side was but 

 little permeable, was, on the English side, quite imper- 

 meable. Owing to this circumstance, they were able to 

 begin at the bottom of the shafts, at 29 m. below the 

 French hydrogr.phic zero, a gallery advancing under the 

 sea by following in 'the stratum an almost regular de- 

 scending slope of i-8oth, or 12 5 mm. per metre. The 

 bed on the English side, somewhat more powerful than 

 on the French side, presents a very great regularity. 

 Thus the Beaumont machine, which has been used in the 

 perforation, has been easily able to trace a -perfectly 

 cylindrical gallery, which has now reached 1800 metres 

 from the shafts, of which 1400 metres are under the sea. 

 So far there has been no access of water. In the banks 

 which form the base of the Rouen chalk, the rock in mass 

 is almost completely dry ; the access of water which has 

 been observed has entirely the character of small springs 

 issuing from the joints of fracture or cleavage. The 

 perfectly cylindrical form produced by the Beaumont 

 machine renders the gallery where such leakage occurs 

 easily isolated by means of cast-iron rings prepared 

 in segments easily united, the rings themselves being 

 clamped together to form a tube of any length. 

 When the water spurts out in considerable force, a 

 sort of mastic or minium is successfully employed, 

 which is placed between the segments of the rock, and 

 compressed in the manner of a water-joint by the pressure 

 of the rings against the rock. The mastic also seems to 

 render the joints of the neighbouring rings water-tight. 

 Owing to the excellent make of these rings, they can be 

 rapidly put in position ; a complete ring can be placed in 

 half-an-hour, and several experiments in the Shakespere 

 Cliff Gallery have proved that by this simple process the 

 springs encountered can be completely blocked. On 

 account of the slope on which the English gallery 

 descends, its extremity recently reached 51 m. below the 

 hydrographic zero, at a point where the depth of the sea 

 at low water is 5 m. ; there is thus 46 m. of chalk between 

 the floor of the gallery and the bottom of the sea. 



NOTES 

 Mr. George GRAY, Honorary Secretaiy of the Philosophical 

 Institute of Canterbury, Christchurch, New Zealand, writes 

 under date May 20 : — "I have been requested to forward you 

 the inclosed resolution passed at a meeting of this Institute May 

 4, 1882, and to ask if you would kindly insert the same in the 

 Notes of your valuable journal. Resolution proposed by C. 

 Chilton, M.A., seconded by G. Gray and carried: — 'That 

 this Institute desires to place on record its high appreciation 

 of the great services that have been rendered to science by the 

 late Dr. Charles Darwin, and its deep sense of the loss that 

 science has sustained through his death.' " 



