38o 



NATURE 



{August 30, 1877 



traces of crinoids, and are the commencement of the Devonian 

 slates, continued hence to Tentagel, and well known as Devonian. 



These few facts seem to verify the general conclusion arrived 

 at by former observers, and, when more fully investigated r.nd 

 the fossils identified, will help to correlate the carboniferous of 

 North Cornwall with the divisions now estabhshed elsewhere. 

 They seem at least to show that there are provinces in our local 

 geology still holding out temptations of further conquest to the 

 geological explorer. 



A'otes on tite Pahron/ology of Flymoiil/i, by R. N. Woith, 

 F.G.S. — This paper did not enter into any controverted ques- 

 tions of stratigraphical geology, but simply noticed the main 

 features of the palaeontology of the limestone of Plymouth and 

 its associated rocks. The Plymouth rocks were commonly 

 classed as Middle Devonian, and consisted of slates, limestone, 

 and slates and sandstones, in order from north to south. The 

 northern slate rocks did not locally contain fossils ; but in the 

 vicinity of Saltash, &c., they did. The Plymouth limestone 

 formed a band nearly half a mile in width and nearly six and a 

 half miles in length. It originated clearly enough in a Tinging 

 coral reef, and in its origin and constitution was therefore essen- 

 tially organic. The rocks on the south of the limestone were of 

 a more complicated character than those on the north. Slates, 

 limestones, shale?, grits, ash-beds and sandstones, alternated 

 with each other in remarkable fashion, while faults and contor- 

 tions by no means solved the riddle. These rocks in part were 

 largely fossiliferous. In the variety of its organic remains the 

 Plymouth limestone was not so rich as most of the other chief 

 limestone districts of South Devon — Wolborough and Barton, 

 for example ; but those that did cccur were for the most part 

 abundant. The leading peculiarity was that while at the western 

 end of the limestone — that was to say, at the Dockyard, Mount 

 Wise, and at Stonehouse, in the quarry behind .St. George's 

 Hall, molluscs of various kinds occurred, at times in great pro- 

 fusion ; at the eastern end of the limestone — Cattedown, 

 Oreston, &c., they were comparatively rare, and over con- 

 siderable areas altogether absent. And in like manner, the 

 branching corals were found chiefly at the western end of 

 the limestone ; and the genuine reef builders at tlie eastern. 

 There did not appear to be any difficulty, however, in accounting 

 for this. Molluscs could only find a habitat on the exterior por- 

 tions of the reef, and it was evident that the eastern section of 

 the limestone more particularly 1 ad been subjected to a consider- 

 able amount of denudation, and that the outer beds had to a 

 large extent been removed. Bivalves and univalves were rarely 

 associated, but kept to distinct areas, where they sometimes 

 occurred in gteat abundance. The peculiar interest of the 

 palteontology of Plymouth consisted in the products of the 

 ossiferous caverns and fissures at Oreston, the Iloe, and Yealmp- 

 ton, including the bones of the mammoth, hippopotamus (?), 

 Rhinoceros tiohorhimis and hMorhiiius^ cave lion, cave hyxna, 

 cave bear, ancient bear, the lesser bison, long fronted ox, horse, 

 ass, &c., and a vertebra of the whale. 



On the Geological Signifrance of the Result of the Boring at 

 Messrs. Menx's Brezvery, 'J'ottenham Court Road, by R. A. C. 

 Uodwin-Austen, F.R.S. — It is now very generally known that 

 this undertaking, after passing through a great thickness of 

 chalk, met with a very insignificant representative of the sands 

 which underlie the chalk in the south-east of England, and 

 thence passed at once into strata which, by characteristic fossils, 

 were identified as of upper Devortian age. This is just as had 

 been anticipated as to the absence of any portion of the oolitic 

 series there,' and confirmed what m.any years since had been 

 supposed to be the subterranean structure of the south of 

 England ; indeed, it may be fairly stated that geologists gene- 

 rally have been of opinion that a band of palaozoic rocks, 

 extending from Westphalia westwards, passel somewhere 

 beneath the secondary formations of the south-east of England. 



The importance o( determining the course of such palrLOzoic 

 band was, that along the whole of the exposed part of its course, 

 as from its extreme eastern place to near Valenciennes, it had 

 dependent on it, on the north, the productive coal-measures of 

 Westphalia, Belgium, and the north of France. From Valen- 

 ciennes westwards the coal-measures are not exposed at the 

 surface, but are reached beneath the chalk foiniation ; but from 

 the underground workings at Douay, Belhune, &c., the relation 

 of the several members of tlie palieozoic series are known to 

 correspond exactly with those where the series is exposed ; as 

 is the case also where they aie again seen at the surface in the 



* See " Report of Coal Commission," vol. i., pp. 431-432. 



Boulonnais, and at sundry other valleys of elevation along the 

 axis of Artois. 



The whole of the coal-measures of Belgium and the north of 

 France must be understood as occupying a trough formed out of 

 the older members of the great paleozoic series, and the explana- 

 tion given of the preservation of this extended and narrow band 

 of coal-growth surface is that it has resulted from a contraction 

 of the earth's crust in a south to north direction, at some time 

 subsequent to the completion of the paleozoic series (coal- 

 measures included), whereby along this line a series of east and 

 west undulations were produced, in the deepest or most con- 

 siderable of which, portions of the coal-growth surfaces became 

 included so as to be preserved during the subsequent periods of 

 denudation and removal. 



From the consideration of the physical features of a line of 

 country of elevation and disturbance, which crosses the European 

 continental area for 300 leagues, it was inferred that like results 

 were due to like causes here ; the line of under-run of the 

 palaeozoic strata was conjecturally carried along by where it has 

 just been met with ; so it may reasonably be supposed that 

 certain other phenomena which in like manner have resulted 

 from the same disturbances should also correspond, and serve 

 for guidance. 



For the present it has not been ascertained in what direction 

 the highly-inclined Devonian strata at Tottenham Court Road 

 were dipping, a most important point in the considerations 

 involved. It may safely be supposed that from their position 

 any palaeozoic rocks at such place must be trending east and west. 

 The occurrence may seem to be an isolated fact, but there are 

 other inferences which tend to give it importance. 



The 653 feet of chalk strata were horizontal, or with only a 

 very slight north dip. The Devonian strata gone through dipped 

 uniformly at an angle of 30^ The section therefore corresponds 

 exactly with those of the north of France. 



In Belgium, and the north of France, it is on the south side of 

 the palxozoic trough that the high inclines occur, as happens 

 along the whole line from Liege to Trelon. On the north the 

 beds are flatter and spread out wider. From this it may be 

 supposed that it was the north side of the trough which was hit 

 upon at Messrs. Meux's, and that it is a trough at this place 

 follows necessarily from the circumstance that the beds so highly 

 inclined were as low as the Devonian. 



Bearing in mind that the^ whole of this part of Europe we are 

 now considering formed part of the area over which the Devonian 

 or lower carboniferous series preceded or was overlaid by the 

 upper or true carboniferous formations, and that where one occurs 

 the other follows everywhere, the fact of the inclination of the 

 beds at Tottenham Court Road involves this, that the higher 

 portions must soon follow — the mountain limestone on the Devo- 

 nian, and the coal-measures on the mountain limestone. 



This reasoning applies equally whether the Devonian strata at 

 Tottenham Court Road may be dipping north or south, but thus 

 much has been ascertained, that London just overlies the edge of 

 a great coal-field, and the probability is that the coal-field lies 

 to the north. 



What seems to suggest that the coal in this direction may have 

 considerable extension is derived partly from a study of the 

 geological features of our own isl.ind, and partly from what is 

 the case in Belgium. It is dependent on what was the original 

 form and extent of the coal-growth surface, and on the places at 

 which the greatest amount of contraction and subsequent denu- 

 dation of the surface took place. 



Mr. Whitaker described the deep borings arounl London, and 

 gave an account of the strata traversed by them. He suggested 

 that some of them should be continued deeper, and thought that 

 in place of a "Sussex boring" or a "Kentish boring" they 

 ought to have a general scheme for investigating the range of 

 the palxozoic rocks. Mr. Lebour suggested that under London 

 (as often occurs in Belgium) the rocks might possibly be inverted 

 or reversed by oblique faults, so that Devonian rocks under 

 certain circumstances might overlie the coal-measures. Mr. 

 Topley, in reply, defended the past action of the Sub-Wealden 

 Committee. 



On a Akiu Method for Studying the Optical Characters oj 

 Minerals, by H. C. Sorby, F.R.S. — The author first described 

 the principles on which this method depended, and showed that 

 the great difference between the appearance seen with the naked 

 eye and the microscope is due to the object-glass being able to 

 collect divergent rays. In looking with a low magnifying power 

 at a small circular hole seen through a section of a crystal, very 

 different phenomena present themselves, according to its optical 



