462 



NATURE 



ISept. 23, 1875 



ing from what is known of the Secondary strata near Boulogne, 

 and comparing them with those exposed in the middle of Eng- 

 land, it was hoped that the Palaeozoic rocks would be reached at 

 a depth not greater than 1,700 feet from the surface. In August 

 1874 the boring had reached a depth of 1,030 feet, and was then 

 delayed in consequence of an accident to the rods. This hole 

 was ultimately abandoned, and a new boring was commenced in 

 February 1875, which has been carried to a depth of 1,812 feet. 

 At this point the work has been stopped, in consequence of great 

 difficulties in keeping the hole clear, and it is not proposed to 

 continue the boring further. From the surface down to 175 feet 

 the strata are shales and impure limestones, with gypsum in the 

 lower part. These beds are referred to Purbecks, and with them 

 are now classed the lowest rocks exposed at the surface, formerly 

 called the " Ashbumham Beds." From 175 to 257 feet the 

 strata are^chiefly sand and sandstones ; these are held to represent 

 the Portland Beds. Below 257 feet there is a great series of 

 bituminous shales and clays, with occasional bands of cement 

 stone and sandstone. Kimmeridge Clay fossils extend down to 

 1,656 feet at least, possibly lower ; so that this formation is here 

 at least 1,400 feet thick. The bottom beds of the boring, just 

 reached, are oolitic in structure, and contain bands of hard lime- 

 stone. To this extent, then, the Secondary rocks have been 

 traversed, and their order and structure ascertained. A disco- 

 very of some commercial value has been made, for two com- 

 panies are in existence to work the gypsum. One of these has 

 been for some time in operation ; a shaft has been sunk and the 

 mineral is now being raised. Scarcely less important is the 

 knowledge now attained that no supply of water can be got by 

 deep wells or borings into the Sub-Wealden strata. As regards 

 the Palaeozoic rocks, the boring has not had the success that was 

 anticipated. The Secondary strata have proved too thick, and 

 there is little or no hope of reaching the older rocks here. A 

 boring is now in progress at Cross Ness by the Metropolitan 

 Board of Works ; this will be carried through the gault, and 

 may possibly throw some light on this question. 



Report of the Committee on Erratic Blocks, by the Rev. 

 H. W. Crosskey. — The Committee continue their record, 

 without attempting the more ambitious task of connecting 

 the facts they report with theories of the history of the Glacial 

 epoch. It will be observed, however, (i) that the facts reported 

 increase our knowledge of the area over which erratic blocks 

 are distributed ; {2) that the boulders are connected together in 

 more definite groups, distinctly pointing to special centres of 

 distribution ; {3) that the possibilities are increasing of obtaining 

 a more exact history of the periods into which the great Glacial 

 epoch must be divided from the grouping and distribution of 

 erratic blocks. Boulders and scratched stones are reported in 

 South Devonshire. New Red Sandstone boulders occur on the 

 left bank of the River Dart, at Waddeton, the largest measuring 

 6X3 feet, at elevations extending from 15 to 200 feet. Are 

 they travelled masses ? If so, whence did they come ? When 

 were they lodged where they now lie ? What was the agent of 

 transportation ? The boulders may have been remnants of New 

 Red beds which once covered the older formations now 

 exclusively overlying the district ; but the different levels at 

 which they are found, the present configuration of the surface of 

 the country, and the great weight of some of them, indicate the 

 possibility of their having been transported by ice from some 

 part of the district lying between Berry Head and Galmpton 

 Common. At Englebourne scratched blocks occur of fine 

 grained trap over an area having slate as its subsoil. Although 

 the size of these boulders renders their mobility under the action 

 of waves possible, yet the grooves upon them appear to indicate 

 ice action with considerable distinctness. A group of small 

 boulders of mountain limestone have been found in the north- 

 east of Hertfordshire, 100 miles from their source in Derbyshire. 

 In Nottinghamshire remarkable boulders have been exposed by 

 a new railway cutting, many of them finely striated, which have 

 been described for the Committee by the Rev. A. Irving. The 

 boulders are of lias, millstone grit, and carboniferous limestone. 

 The boulders of lias limestone are derived from the liassic strata 

 of the immediate neighbourhood upon which they chiefly lie. 

 The nearest millstone grit is formed at Castle Donnington and 

 Stanton-by-Dale in Derbyshire, on opposite sides of the Trent 

 Valley ; the former place twelve miles south of west, the latter 

 twelve miles north of west from the deposits in which they occur. 

 The nearest carboniferous limestone corresponding to that of the 

 boulders is found at Ticknall in Derbyshire, about eighteen miles 

 distant south of west. The height of the group above the sea 

 is about 200 feet. The extent of the boulder clay and deposit is 



at least several square miles. In the cutting between Plumtree 

 and Stanton the boulders are largest and most numerous, and 

 are mingled with an immense number of quartzite pebbles, the 

 whole being compactly bound together. In Leicestershire, there 

 is no doubt, Charnwood Forest was a centre of distribution by ice, 

 of blocks of all sizes. The position of various boulders is reported 

 seven miles from their source, together with a block of peculiar 

 millstone grit, at Hoby, near Melton, which must have come 

 from Durham or Northumberland. In Worcestershire (Broms- 

 grove district) ninety-three boulders have been examined, many 

 of them of considerable size, consisting chiefly of varieties of 

 felspathic rock. It is impossible as yet to generalise on their 

 distribution, but it is noticeable that no specimens of granite 

 have been observed in this district, although they occur so 

 abundantly around Wolverhampton. A list is given of the size 

 and position of the principal erratic blocks, which are rapidly 

 being destroyed. The group of felspathic boulders extends 

 through Northfield and King's Norton to Birmingham. Isolated, 

 and in many cases striated, boulders are reported in the neighbour- 

 hood of Liverpool, including blocks of greenstone, syenite, 

 felspathic ash, &c. On the north-west of Bradford a few 

 boulders are reported, similar to the rocks at Scaw Fell, Cumber- 

 land, and containing small garnets. The destruction of erratic 

 rocks is going on so rapidly through the country that the Com- 

 mittee earnestly request that reports may be forwarded to them 

 of their occurrence. Some are being buried to get them out of 

 the way of the farmers ; others are built into walls, made the 

 foundations of houses, or blasted into fragments. In some cases 

 they constitute the foundations of church towers. A timely 

 record will preserve many facts of large import and assistance in 

 the discussion of problems connected with the centres of ice 

 action, the range of the land ice, the courses of icebergs, and the 

 existence of interglacial epochs. 



SECTIONAL PROCEEDINGS. 

 SECTION A — Mathematics and Physics 



On the Measurement of Wave Motion, by Prof. Frederick 

 Guthrie. — The rate of progression of a wave in a liquid of 

 infinite depth and extent depends upon the wave length ; 

 scarcely at all upon its height, and not at all upon either its 

 breadth or the density of the liquid. The measurement of 

 rate of wave-progression in open water is difficult and at 

 best inaccurate. Natural waves generated and supported 

 or restrained by wind have abnormal rates of travelling. 

 Artificial waves in ponds degenerate rapidly in height 

 and increase in wave length, and so in wave progress- 

 rate. The time required by a wave generated in the 

 middle of a pond in reaching the edge, is dependent on its mean 

 wave length. Perhaps after reflexion from the edge the con- 

 ditions are sequentially reversed, and the time occupied in return- 

 ing is equal to that of departure. Perhaps not. I think not, 

 because the increase of wave length (and therefore of wave 

 progress) is a function of the height. Be this as it may, many 

 sources of error are got rid of by using troughs of limited sur- 

 face and indefinitely great depth, by causing the original and 

 reflected wave so to interfere as to produce one or more nodes ; 

 and instead of measuring the time required for the crest of a 

 wave to travel in a straight line over a given distance, by mea- 

 suring the number of times the crest of the wave system reap- 

 pears in the same place in a given time ; in other words, by 

 transferring to liquid waves the method used to measure the 

 rate of sound in solid bodies. As far as the method is trust- 

 worthy we get by means of a trough whose diameter is one 

 or two feet, a more accurate method of measuring the rate of 

 wave progress than by an experiment in an ideal pond a mile 

 across. 



Experiment shows that if a concentric binodal wave system be 

 generated in a cylindrical trough of water of more than a certain 

 depth (say half its diameter), the following conditions hold good. 

 A nodal ring is formed at one-sixth of the diameter from the cir- 

 cumference. The amplitude at the centre is double that at the 

 circumference unless the disturbance is very great. The rate of 

 undulation — that is, the number of times in a given time that the 

 crest appears in the centre — does not depend sensibly upon the 

 amplitude, nor upon the temperature, nor upon the density of the 

 liquid. It depends almost wholly upon the wave length of the 

 waves formed — that is, upon the diameter of the trough — and is 

 identical with the number of beats of a pendulum whose length 

 is equal to the radius of the trough. Hence the rate of undu- 

 lation varies inversely as the square root of the trough radius or 



