558 



NATURE 



[October 6, 1898 



GEOLOGY AT THE BRITISH ASSOCIATION. 



CO far as Section C was concerned, the Bristol meeting of the 

 "^ British Association was decidedly successful. The attend- 

 ance at the sectional meetings was above the average, and the 

 interest well sustained, a larger proportion than usual of the 

 papers and reports being of a character to give rise to discussions 

 on broad general principles, for which these occasions are pre- 

 eminently adapted. 



In some cases these discussions were curtailed from lack of 

 time, and there was a little discontent among the more steadfast 

 adherents to the indoor work of the meeting that the whole of 

 the papers should have been crowded into four days, and the 

 Saturday and Wednesday half-day sessions dispensed with. But 

 .in a region so rich in geological interest it was desirable that 

 every opportunity for outdoor investigation should be given to 

 the members of the Section, especially as the weather during the 

 meeting was. singularly favourable for field-work. The popu- 

 larity of the short afternoon excursions arranged for Friday, 

 Monday and Tuesday, under the leadership of Prof C. Lloyd 

 Morgan and Mr. H. Pentecost, to classical sections in the 

 vicinity of Bristol, proved that to the visiting geologists the 

 chance of inspecting the best exposures under competent 

 guidance was at least of equal importance to the indoor pro- 

 ceedings. These afternoon excursions have, during the last 

 three or four years, become an important feature in the arrange- 

 ments of the Section, and though it has been sometimes objected 

 that they are detrimental to the attendance indoors during the 

 later stages of the daily session, it is doubtful whether such be 

 really the case. The difficulty of holding together an audience 

 of notable dimensions when the sitting of the Section is pro- 

 longed late into the afternoon was felt at these meetings long 

 before the institution of the short excursions. 



The papers and reports submitted to the Section are too 

 numerous for adequate mention, and special reference can only 

 he made here to such as possessed wide interest or led to much 

 debate. As frequently happens, some of the papers containing 

 the most solid and original work attracted the least discussion. 



At the opening day of the sectional meeting, after the 

 presidential address, Prof. C. Lloyd Morgan gave a clear 

 general account of the more interesting features of the local 

 geology, dealing especially with the places to be visited during 

 the excursions. The lantern slides by which this address was 

 illustrated were unfortunately almost invisible owing to the 

 insufficient darkening of the room. 



Mr. E. Wethered followed with a paper on "The building 

 of the Clifton rocks," in which he contended for the im- 

 portance of certain micro-organisms in the formation of the 

 local limestones. These " incrusting organisms," along with 

 other forms which he described, all hitherto usually held to be 

 of inorganic origin, are regarded by Mr. Wethered as organic 

 growths, to which in some cases the structure of the limestone is 

 due ; and these he considers to be serviceable aids in identifying 

 the strata. At a later session Mr. Wethered brought forward a 

 second paper on " The work of incrusting organisms in the 

 formation of limestone," in which he urged the claims of 

 Girvanella and allied forms in the production of the oolitic 

 structure in Jurassic rocks. Both papers were illustrated by 

 beautiful lantern slides of rock-slices prepared by the author. 

 These papers gave rise to lively discussions, in which by some 

 speakers the organic origin of some of the structures was strenu- 

 ously denied ; in his able reply, Mr. Wethered claimed that 

 a thorough investigation of his slides by a committee of experts 

 would convert the partial recognition which his views had already 

 won into a thorough-going acceptance of all his conclusions. 



Mr. A. Strahan brought before the meeting an account of the 

 results of the revision of the South Wales Coal-field by the 

 Geological Survey, showing the great advances which have been 

 made in our knowledge of the structure of this important area, 

 and the methods adopted for representing the new information 

 upon the maps. 



In a paper on "The comparative action of sub-aerial and 

 submarine agents in rock decomposition," Mr. T. H. Holland, of 

 the Geological Survey of India, drew attention to the wide- 

 reaching difference between the manner of decomposition of the 

 crystalline and igneous rocks in Southern India and in Europe, 

 especially in the degree of hydration of the minerals. This 

 difference, he thought, might be due to the absence of sub- 

 marine action in the central portion of Southern India during the 

 later geological periods, so that the rocks have been affected 



NO. I 5 10, VOL. 58] 



only by sub-aerial weathering, and deeper portions of the earth's 

 crust have, by long denudation, been exposed at the surface 

 than in Europe. 



Friday's session was opened by a suggestive discourse by 

 Prof. O. C. Marsh, on "The comparative value of different 

 kinds of fossils in determining geological age," in which the 

 claims of the vertebrates, wherever they existed, were pressed as 

 being the best for the purpose. As a side-issue. Prof. Marsh drew 

 renewed attention to the Jurassic affinities of the English Wealden 

 fauna, so that his paper provided almost unlimited scope for 

 discussion. Most of the speakers on the subject, while acknow- 

 ledging that the main point of Prof. Marsh's contention might be 

 theoretically correct, dwelt upon the practical difficulties to the 

 field-geologist in the collection and determination of vertebrate 

 remains, and urged that this must prevent these fossils being 

 used for zonal purposes except in rare instances. Another 

 paper which provoked an interesting discussion was that of 

 Prof. J. F. Blake, on " Aggregate deposits and their relation to 

 zones." The author proposes the term "aggregate deposits" 

 for strata in which fossils characterising more than one zone 

 occur together in the same rock-band. He considers that in 

 such deposits the fossils do not lie in their natural position, but 

 have been swept together tumultuously by strong currents. In 

 the debate on this paper, while general approval of the term 

 "aggregate" was expressed, there was much difference of 

 opinion as to the manner in which such deposits had accu- 

 mulated, and it was suggested that Prof. Blake had included 

 strata of diverse origin in his proposed classification. 



The two papers contributed by Mr. T. Groom, on " The age 

 and geological structure of the Malvern and Abberley Ranges," 

 were good examples of careful stratigraphical investigation, and 

 were well received. Mr. Groom's conclusions are that the 

 Malvern axis was not an island in Cambrian and Silurian seas as 

 generally supposed, but that it was elevated chiefly by Upper 

 PaliTeozoic crustal movements and its folds belong to the Great 

 Hercynian system formed towards the close of the Carboniferous 

 Period. At the same session Mr. E. Greenly announced the 

 discovery of Arenig shales beneath the Carboniferous rocks near 

 the Menai Bridge, and in another paper described a clear case 

 of boulder- uplift at Llandegfan, Menai Straits, where a train of 

 blocks has been raised about 300 feet in the distance of one mile. 

 Mr. Greenly also called attention to the impending destruction 

 by quarrying operations of the most important portion of the 

 drift section of Moel Tryfaen, and his suggestion that a com- 

 mittee should be appointed for the purpose of securing, while 

 there was yet lime, photographic and other records of this cele- 

 brated section was at once acted upon, and a small grant was 

 obtained to cover the expenses. 



In his paper on " The age and origin of the granite of 

 Dartmoor, and its relations to the adjoining strata," Mr. A. 

 Somervail put forward the view that the intrusion of the granite 

 in question took place after the folding of the Lower Culm 

 strata, but before the Upper Culm series was deposited. In 

 the discussion, while the importance of Mr. Somervail's con- 

 clusions was acknowledged, the speakers generally expressed 

 themselves unable to form an opinion until the fuller details 

 of the sections on which the author based his views should be 

 published. 



The first paper taken on Monday was that of Mr. R. 

 Etheridge, on " The relation and extension of the Franco- 

 Belgian Coal-field to that of Kent and Somerset." After 

 reviewing the history of the discovery of coal at the Dover 

 boring, where it is expected that the Coal Measures will shortly 

 be reached by the shafts now being sunk, Mr. Etheridge pro- 

 ceeded to discuss the general bearing of this discovery and the 

 probable extension of the southern coal-fields under the Secondary 

 rocks. A new section recently obtained by a deep exploratory 

 boring at Brabourne, near Ashford, was then described, where 

 after passing through Lower Greensand, Wealden, Portlandian, 

 Kimeridge Clay, Corallian, Oxford Clay, Lower Oolites, and 

 Middle and Lower Lias, red conglomerates believed by the 

 author to be Old Red Sandstone have been encountered at a depth 

 of 1875 feet from the surface. The Jurassic strata in this section 

 are about 450 feet thicker than at Dover. In the discussion on 

 this important paper, Prof. Boyd Dawkins and Mr. W. Whitaker 

 both expressed doubts whether the Old Red Sandstone age of the 

 lowest portion of the Brabourne section could be considered 

 sufficiently established ; and the former speaker stated that he 

 fully expected some of the Kentish borings would draw blank, 

 but others would succeed, and all would supply valuable in- 



