472 



NATURE 



[April 11,1872 



but we were hardly prepared until lately to learn how rapid the 

 variation in their thickness is. Mr. Hull ha-i now shown that 

 the Groat and Inferior Ooli'es thin out from a thickness of 

 792 feet in Glouc stershire to 205 feet in Oxfordshire, ami ihe 

 Lias and Trias from logo fest to 400 (?) feet ; while in I;ke 

 mmner tlie Tr as decreases from 56X) feet in Lancashire and 

 Clieshire, to 2O0O in Staffordshire, and 600 feet in Warwickshire. 

 We also know thit on the northern flank of the Mendips, the 

 Trias, Lias, and Oolites tail off, although their dimensions in 

 Gloucestershire are so considerable. It would appear that all 

 the Secondary rocks, excpt those of the Cretaceous series, show 

 a distinct th'nning-out in their range southward, which is doubt- 

 less due to the existence of an old pre-Tiiassic land on the 

 south — such as would have been formed by the prolongation of 

 the PahEozoic rocks of the Ardennes and Mendips through the 

 south of Englan 1. It has been urged, on the o her hand, that 

 this thinning-out is a proof of the existence of a still older land in 

 that area ; but as the argument is bised on the evidence of rocks 

 of po:-t-Carboniferous age, it is clear that, whether the land were 

 of Cambrian and Silurian, or of Devonian and Carboniferous 

 age, the result, as affecting the Secondary rocks, would be the 

 same. 



Thii thiiiningout of the Secondary strata has now been proved 

 not to be merely hypothetical. At three points, on or near the 

 presumed line of the oil underground range, the Tertiary and 

 Cretaceous strata have been traversed in well-sections, and 

 Palaeozoic rocks found to underlie them at once, with >ut the 

 intervention of any Triassic, Liassic, or Oolitic stra'a. Thus at 

 London the presence of red and grev Sand.--tones, apparently of 

 PaUieozoic age, has been proved under the Chalk at a depth of 

 l,iI4fe!-t. Again, at Harwich and at Calais, strata of early 

 Carboniferous age liave been found ako immediately un'er the 

 Chalk, at depths respective'y of 1026 and 1032 feet. There is 

 therefore reason to believe that the underground ridge of the 

 Menihps an 1 the Ardennes pas-es i 1 a 1 ne l^rom Frome through 

 North Wiltshire, Berkshire, Middlesex, North-east Kent, and 

 between Calais and Boulogne, at a depth beneath the Secondary 

 strata of not more than from 1000 to 1500 feet, while the coal- 

 troughs, which may flank this range on the north would, judging 

 from the analogy of the structure and reUtion> of the same rocks 

 at Mous and Valenciennes, be met with at depths very little, if 

 at all, greater. 



To the north of this area it is provable that the thickness of 

 the overlying rocks is greater ; but we have no m 'ans of knowing 

 exicily. In Northamptonshire the Great and Inferior Oolites 

 and the Lias have been found not to exceed together 8S0 feet, at 

 which depth the New Red Sandstone was reached ; but its 

 thickness was not proved beyond 87 f:et ; while at Rugby, the 

 Lias was found to be abjut 905 feet thick, below which 136 feet 

 of beds of New Red Sandstone were parsed through. Looking 

 at the proved thinning out fruin north to soudi of the New Red 

 and Permian strata, there is no reason to suppose that they 

 would be found of any very great thickne-s in the southern 

 counties. Even immediately to the s 'Ulh of the known coal- 

 fields of the Midland counties, the trials for coal have not yet 

 proved any very great thickness of these rocks. It would seem, 

 in fact, that the extensive tracts of Chdk. Oolites, and Trias, 

 forming the substrata of our Midland and Southern counties, 

 constitute but a compara ively shallow crust filling up the plains 

 and valleys of Palaeozoic rocks, the great framew.'rk of which 

 stretches apparently at but a moderate depth under our feet, and 

 of which the highest ridges only, such as those of the Ardennes 

 and Mendips, now rise a ove ground. 



It is clear, therefore, that in any search for coal, the relation 

 of the Second .iry and the Palaeozoic groups of rocks to one ano'her 

 being perfectly independent, the latter must be considered 

 entirely on their own internal evidence, and apart from the 

 bearing of the newer rocks covermg ihcm and forming the pre- 

 sent surface, except po sihly in a feAi cases where o-d lines of 

 disturbance have proved poiiits of least resistance, and yielded 

 again, as sugge>ted h\i Mr. Godwin-Austen, to later movements, 

 which have equally affected the overlying formations. 



It may be asked if any corrclaiion can be established between 

 the coal-measures of Bristol and South Wales and those of 

 France and Belgium. So far as the identity of any particuhr 

 bed of coal or of rock, it is impossible, and we should not ex- 

 pect it ; for the vari dion in all 'he he's of any coal-basin is well 

 known to be so great and ra|>id, that in the different parts of the 

 same basin it is often difhcult, and sometimes impossible, to 

 establish any correlation ; while in adjacent basins, such as those 



of Wales and Bristol, or of Hainaut and Liege, such attempts ,\ 

 have, with few exceptions, hitherto utterly failed. There are, ; 

 hovever, more general fea'ures which serve to show, at all 

 events, some relationship. The great dividing mas> of from | 

 2.O00 to 3 GOO feet of rock called Pennant exists in both the ; 

 Welsh and Bri.tol coal-field; and the total mass of coal-mea- 

 sures is not Very different, it being 10,000 to 11,000 feet in the 

 one, and from S,ooo to 9,000 in the other, and there being in 

 Wales 76, and in .Somerset 55 workable seams of coal. In the ■ 

 Hainaut (or Mons and Charleroi) basin, the Measures are 9,400 

 feet thick, with no seams of coal; in the Liege basin 7,600 

 fee', wiih 85 seams; and in Westphalia 7,200 leet, with 117 

 seams. On the other hand, none of our central or northern 

 coal-basins, with the exception of the Lancashire field, exceed 

 half I his thickness, and more generally are nearer one fourth. 

 Further, the marked difference which exists between the northern 

 coals and tho^e of Wales and .Somerset, the preponderance of ' 

 caking-coals in the north, and of an'hracite, steam, and smiths' 

 c >al in the south, equally exists between our nortliern coals and 

 those of Belgium, which latter show, on the other hand, close 

 affinities with those of Wa'es and Bristol. I am informed by 

 two experienced Belgian coal-mining engineers and good geo- 

 logists, who have twice visited our coal-districts, that the only ' 

 coals they found like those of Belgium were the coals of South ' 

 Wales and Radstock — there was the same form of cleavage, the 

 same ch iracter of measures, and the same fi ness for like econo- 1 

 mical purposes. Organic remains help us but little, but too 

 little is yet kn lA'n of their rela ive distribution. The plants are, 

 as usual, the same ; so also are shells of the genus Aiithracosia, ' 

 and a number of small Enloinostraca ; whde there is a scarcity 

 of many of the marine forms which are more common in some \ 

 of our central and northern fields. That, therefore, which best 

 inilicates the rela'ion between the coil-fields of the south-west j 

 of Englaid and those of the north of France and Belgium, ij ' 

 the similarity of mass and structure, uniformity of subjection to 

 hke physical causes, and identity of relatii n to the underlying 

 older and to the overljing newer formatioi s. 1 



It was in the north that the conditions fitted for the formation i 

 of coil first set in. The common Stiginaria ficoidcs and various 5 

 Coal Measure pl.ints appear at the base of the Carboniferous or ,, 

 in the Tuedian series of Northumberland, which there overlies •. 

 conformably the Upper Old Red Sandstone ; and productive 

 beds of coal exist low down in the Mountain- Limotone series. 1 

 These disappear in proceeding suuthward, and the great produc- 

 tive coal-series becomes confined to beds overlying the Mdlstone 

 Grit. If the coal-growth set in earlier in the north, it seems to 

 have been prolonged farther south, under more favourable con- 

 ditions, to a later period. What those conditions were — whether 

 the proximity of a greater Iind-surface, of a I-mg r and greater 

 subsidence, with more numerous rests — we cannot yet pretend 

 to say. 



Of the prolongation of the axis of the Ardennes under the 

 south of England there can be little doubt ; nor can there be 

 much doubt that the same great contortions of the strata, which ■ 

 in Belgium placed the crown of the anticlinal arch at a height of , 

 four or five miles above the level of the base of the accompany- : 

 ing s\nclinal trough, to the bottom of which the Coal MeasureSj \ 

 descend, and was the cause of similar folds in the Coal Measures '. 

 of Somerset and Wales, were continued along the whole line of ! 

 disturbance, and that the preservation of detached portions of the 

 same great supplementary trouih is to be looked for under- . 

 ground in the immediate area, just as it exists above ground in 

 the proved area ; for the minor subordinate barriers dividing the 

 coal-basms can, I c 'Uceive, in no way permanently affect the . 

 great master disturbance, by which the presence of the Coal 

 Measures is ruled. Whether, however, admitting that the Coal 

 Measures were originally present, they have been removed by 

 subsequent denudation is another question. 

 ( To be continued. ) 



SC/ENT/F/C SE RIALS 

 Annakn der Chetiiieund Pharmacie, December 1871. A con- 

 siderable part of this number is occupied by a valuable paper 

 " On valeric acids from different sources," by Erlenmeyer and 

 Hell. They prepared isobutyl iodic acid, and from this the corre- 

 sponding iodide, which they treated with alcoholic potash to con- 

 vert it into potassic valerate ; the valeric acid from these reactions 

 had no action on polaiised li|,;ht. They prepared valeric acid 

 from valerian root, and this also had no rotating action on a 



