Sept. 14, 1882] 



NA JURE 



491 



wire, which pastes through the mercury into the gaseous space. 

 It theie makes contact between the mercury below, and a smaller 

 quantity in an insulated capsule within the tube. '1 he lever is 

 worked from the outside by mere contact with the escapement 

 wheel of an ordinary clock, « Inch o\\ ing to its extreme sensitive- 

 ness is quite sufficient to do this. The positive and negative 

 poles of the terminals are connected respectively with the 

 mercury in the capsule and that in the vessel. It is evident that 

 although the lever is always in electrical contact with the mercury 

 in the vessel, the circuit is only completed when it is brought into 

 contact with that in the capsule. 



Varit u> experiments have been made with this instrument, and 

 the result has been completely satisfactory. With a battery of 

 fifteen Grove cells the surface of the mercury was brighter at the 

 end of half an hour than at the beginning of the experiment, 

 although a much more brilliant spark was visible than when 

 eonlact was made in air. Af:er three weeks ( f intermittent 

 working for 1 eriods of sometimes as much as twelve hours 1 at 

 with weaker batteries, the mercury remained qui'e clean. 



The present form of the instrument is shown in the annexed 

 figure. The general action is similar to the one already described 

 A, being the gaseous space, D, the capsule of mercury, E, the 

 escapement wheel. The chief improvements to be noted are : — 



1. Con'act is made and broken at F instead of at n, thus pre- 

 venting sensible loss by volatilization from the small quantity of 

 mercury in the capsule. The wire D F is insulate! from the 

 bent lever by the glass junction at 11. 



2. Portability is secured by having a plug, K, shown in dotted 

 lines, which can be screwed down and a gland L, by means of 

 w hich the wire can be packed by an india rubber washer, M. 

 The lever and balance weights, \v w, arc made to go within the 

 lid which can be taken off the bottom and screwed on to the top 

 (as shown by the doited lines). This keeps in any loose mercury 

 above the plug. 



3. The lever is so arranged that contact is only of momentary 

 duration, a point of no little importance in connection with the 

 constancy of the battery. 



SECTION C— Geology 



On the Geology of the Channel Tunnel, by Prof. \V. Boyd 

 Dawkins, F.R.S. — He laid special stress on the fact that the 

 line of faults both on the English and French coast are small, 

 neither of them have throws of more than 3S feet, and even this 

 magnitude is rare, he therefore considers the ,-hances of the 

 older porous rocks being throw n by them is well nigh impossible. 

 He considers, however, that in some cases this fault acts as ducts 

 onveying water downwards, and he ascribes to one of these 

 faults the well-known springs on Abbot's Cliff, known as the 

 " Lydden Spout." 1. The lower beds of the chalk marl and 

 the lower part of the grey chalk, are the only strata in the chalk 

 sufficiently impervious to alloiv of the construction of a tunnel in 

 the dry. 2. That the ou'erop of the chalk marl between Folkestone 

 and the Shakespeare Cliff, is the best position for a tunnel, which 

 could strike the lower part of the chalk marl, and remain in it 

 throughout, so as to join the workings of the French Channel 

 Company, which are being carried on in the same horizon. 3. 

 That the faults in the lower | art of the chalk would not now allow 

 of free percolation of water, and are not likely to become a serious 

 obstacle to the work. 4. That the sttata above the chalk marl 

 are so porous and traversed by open fissures that they allow of 

 free acce-s to water both sub-aerial and marine. He c ■> siders 

 that on ths French siele the recks are far more shattered and 

 faulted, and more open to be traversed by water, which is now, 

 however, being successfully contended with by the French Com- 

 pany. The author refers to analy.-es made of samples of cre- 

 taceous rocks. Insoluble material in gault was 45 per cent.; 

 chalk marl (No. 1), 75 per cent. ; and only 6 per cent, in the 

 more soluble part of the grey chalk; over the yellow chalk IS 

 per cent. ; while above this it is only 2 per cent, in the lower 

 white chalk without flints. He described the work done by 

 Sir John Hawkshaw in having soundings taken in the English 

 Channel to ascertain the character of the Channel bottom. 



On tin- Proposed Channel Tunnel in its Geological Aspeets, by C. 

 E. De Kance, F.G.S., described the sub-divisions found in 1874m 

 the chalk of Abbott's Cliff, by Mr. Hilton Price and himself, and 

 the impermeable nature of the lower beds, which support a sheet 

 of water met with in springs at the outcrop, and in wells at 

 various points. He regards these underground waters as circu- 



lating in tie por. us white chalk under the :ea, and he con- 

 siders that the artificial abstraction of water by pumping, in 

 making the proposed tunnel in St. Margaret's Bay, w ill allow 

 the percolation of sea-«ater to the extent of a million gallons 

 of water ini ach mile driven daily, and therefore offers great diffi- 

 culties in the way of the construction of a sub-marine tunnel 

 which nre not pre-ented by the lower beds of the chrlk marl. 



Evidence of Wove Aetion at a Depth of 40 Fathoms in the 

 English Channel, by A. R. Hunt, B.A., describes 16 localities 

 in which pebble have been dredged off the Start Point in 34 

 fathems of water, and the discovery of a soda water bottle 

 covered with Sen ula*, and containing 36 species of shells » hich 

 have teen washed in, at a depth of 40 fathoms, by a Brixham 

 trawling fishing boat. 



List of Works on the Geology and Paleontology of Oxfordshire, 

 Berkshire, and Buckinghamshire, by W. Whitaker, B. A. — This is 

 a continuation of the County or District Lists, of which a cata- 

 logue was given at the head of the Welsh List in the Report for 

 1880 ; the present list contains nearly 300 references. 



On the Equivalents in England of the "Sables de Bracheux" 

 and of the Southern Limits of the Thanet Sands, by J. Prestwich, 

 M.A., F.R.S. — The author dwells on the importance of esta- 

 blishing in adjacent separate basins, a certain number of well- 

 defined horizons. The lignitic and freshwater beds of the Paris 

 Basin, and of the Woolwich and Reading series, form one such, 

 but he considers the correlation of the beds beneath to be not 

 yet satisfactorily e-tahlished. The author correlates the Man- 

 cheux sands with the lower ends of the Woolwich series, and he 

 is confirmed in this view by M. Doharges, and be fuither 

 is of opinion that the Thames sands are ab ent in the Paris 

 Basin. 



( // the Formation of /-lints, by Prof. W. J. S, .lias, M.A.— 

 feints are siliceous pseudomorphs after chalk. Three different 

 stages in tl eir formation are to be distinguished : (1) the silici- 

 Bcation of the foraminifera, c ccoliths, and calcareous granules 

 of the chalk gives rise to siliceous chalk; (2) a deposition of silica 

 follows and 1 roduces white or grey flint ; (3) as the deposition 

 of silica continues it fills up and obliterates the pores of the 

 opaque grey flint, tendering it black and translucent, thus the 

 common Hack flint re ults. Flint nodules are sometimes found 

 in which all three singes are still represented, but more frequently 

 only the last two : thus grey spots and blotches are seldom 

 ab-ent from black Hint, whilst in many ca-es the two kinds 

 regularly alternate and thus produce the phenomenon of banded 

 flint, wlvch has up to this time remained without any satisfactory 

 explanation. 



On some Fossils from the Inferior Oolite, by the Rev. G. F. 

 Whidbotue, M.A , and I'rof. W. J. Sollas, M. A.— Describes 

 bivalve shells of mollusca chiefly in the Jermyn Street Museum, 

 and 8 new species of sponges, of which 4 belong to 4 new 

 genera. 



Mention of an Example of an Early Stage of Metamorphic 

 n an Old Fed Sandstone Conglomerate near Aherfoil, 

 by Prof. James Thomson, LL.I'., F.R.S., describes fractured 

 quartzite pebbles which he regatds as originally a plastic body, 

 which first bent, and then broke, and that the present brittle 

 appearance has been induced at a late era, and he refers their 

 origin to metamorphic action. 



On Features in the Glacial Workings noticed on Sandstone 

 Conglomerate at Skelmoi lie and Aherfoil, by Prof. James Thomson, 

 LL. D., F.R.S., describes a railway cutting half a mile from 

 Aberfoil. At 150 to 2CO feet above the sea occurs striated 

 sandstone, on which were glaciated pebbles, behind which 

 occurred tails of fine material, 5 or 6 feet in length, in the direc- 

 tion in which the ice travelled. Examples have been found by 

 the author showing distinct traces of the ice moving up hill. 



Problems in the Geology of the Channel Islands, by the Rev. E. 

 Hill, M.A., stales the work done by the late Prof. Ansted leaves 

 much to complete, and is of opinion that there is here a fine 

 field for detailed investigation. 



Notes on the Geology and Mining- of the United States of 

 Columbia, S.A., by R. B. White.— This paper gives an ex- 

 haustive report of the range of metals in time and space in this 

 region, and the application of facts observed, to other districts. 



Suggestion for a Revised Classification of the British Eocene, 

 by J. S. Gardner. — Somen odification in the classification of the 

 Eocene has become desirable, through the transfer of the Upper 

 Eocene group of Edward Forbes to the Oligocene formation. 

 The discovery of several distinct floras seems alsD to necessitate 

 certain alterations in order to bring periods founded originally 



