48o 



NA TURE 



[September 15, 1S98 



has produced both the Jurassic and Cretaceous escarpments as 

 well as the numerous gorges which add so much to the interest 

 of the scenery. These phenomena have been well described by 

 Prof. Sollas (/'riJf. Geol. Assoc, vol. vi., l88i, p. 375), when 

 he directed an excursion of the Geologists' Association in 1880. 

 Should any student wish to know the origin of the gorge of the 

 Avon at Clifton, for instance, he will find in the Report an 

 excellent explanation of the apparent anomaly of a river which 

 has been at the trouble of sawing a passage through the hard 

 limestone, when it might have taken what now seems a much 

 easier route to the sea by way of Nailsea. 



The origin and date of the Severn valley is a still bigger 

 question, and this was broached by Ramsay, some five-and- 

 twenty years ago, in a suggestive paper on the River Courses of 

 England and Wales {Quart. Jour. Geol. Soc, vol. xxviii,, 1872, 

 p. 148). He there postulates a westerly dip of the chalk sur- 

 face, which determined the flow of the streams in a westerly 

 direction towards the long gap which was being formed in 

 Miocene times, near the junction of the Mesozoic with the 

 Palaeozoic rocks. The still more important streams from the 

 Welsh highlands had no doubt done much towards initiating 

 that gap ; and by the end of the Miocene period, if one may 

 venture to assign a date, the valley of the Severn, which is one 

 of the oldest in England, had already begun to take form, 

 though many of the valleys of Wales are probably much older. 



We may now be supposed to have arrived at a period when 

 the physical features of this immediate district did not differ 

 very materially from what they are at present. The great Ice 

 Age was in full force throughout Northern Europe, and, 

 according to views which meet with increasing favour, the 

 German Ocean and the Irish Sea were filled with immense 

 glaciers. What was taking place at that time in the estuary of 

 the Severn? 



This is a case which requires the exercise of the scientific 

 imagination, of course under due control. There is probably 

 nothing more extraordinary in the history of modern investiga- 

 tion than the extent to which geologists of an earlier date per- 

 mitted themselves to be led away by the fascinating theories of 

 Croll. The astronomical explanation of that "will o' the 

 wisp," the cause of the great Ice Age, is at present greatly dis- 

 credited, and we begin to estimate at their true value those 

 elaborate calculations which were made to account for events 

 which in all probability never occurred. Extravagance begets 

 extravagance, and the unreasonable speculations of men like 

 Belt and Croll have caused sonie of our more recent students 

 to suffer from "the nightmare." 



Nevertheless Croll, when he confined his views to the action 

 of ice, showed himself a master of the subject, and his sug- 

 gestions are often worthy of attention, even when we are not 

 convinced. Writing in the Geological Magazine in 1 871, he 

 points out that the ice always seeks the path of least resist- 

 ance ; and he refers to the probability that an outlet to the ice 

 of the North Sea would be found along the natural hollow 

 formed by the valleys of the Trent, the Warwickshire Avon, 

 and the Severn. Ice moving in this direction, he says, would 

 no doubt pass down into the Bristol Channel and thence into 

 the Atlantic. Again {o/>. cit. Dec. 2, vol. i., 1874, p. 257), 

 referring to the great Scandinavian glacier, he says, " it is 

 hardly possible to escape the conclusion that a portion of it at 

 least passed across the south of England, entering the Atlantic 

 in the direction of the Bristol Channel." These views were 

 not based on any local knowledge, but merely on general con- 

 siderations. The problem as to whether there are any traces 

 of the passage of such a body of ice in the basin of the lower 

 Severn must be worked out by local investigators. Irrespective, 

 too, of the hypothetical passage of a lobe of the North Sea 

 glacier, we are confronted by a much more genuine question, 

 namely, what was the possible termination towards the south of 

 the great body of ice with which our more advanced glacialists 

 have filled the Cheshire plain ? 



A recent president of the Cotteswold Field Club, of whom, 

 imfortunately, we must now speak as the late Mr. Lucy, took 

 a lively interest in the Pleistocene geology of the district, and 

 his papers in the Proceedings of the Cotteswold Field Club have 

 always attracted attention. His map of the distribution of the 

 gravels of the Severn, Avon, and Evenlode, and their exten- 

 sion over the Cotteswold hills, prepared in conjunction with 

 Mr. Etheridge, is a valuable contribution to the history of the 

 subject {Proc. Cottes. Nat. Club, vol. v, pt. ii., 1869, p. 71). 



NO. 1507, VOL. 58] 



Again he wrote on the extension of the Northern Drift and 

 Boulder-clay over the Cotteswold Range {op. cit. vol. vii. 

 pt. i., 1878, p. 50), and on this occasion described the interest- 

 ing section in the drifts presented by the Mickleton tunnel. In 

 his previous paper, Mr. Lucy had carried the drifts with nor- 

 thern erratics to a height of 750 feet, but he now claimed that 

 " the whole Cotteswold Range had ceased to be dry land at the 

 time the Clays and Northern Drifts passed over it." We per- 

 ceive from this passage that Mr. Lucy was a " submerger," and 

 in this respect differed from Croll, who most probably would 

 have attributed the phenomena to the action of his great ice- 

 lobe traversing the south of England. 



The question which more immediately concerns us relates to 

 the value of the evidence which would require either a glacier 

 or a " great submergence " to account for these things. The 

 alleged phenomena are in many cases capable of other inter- 

 pretations. We have the authority of Mr. Etheridge that little 

 or no true Boulder-clay occurs in the Cotteswold area (,Proc. 

 Cottes. Nat. Club, vol. xi., 1893, p. 83). On the other hand, 

 the distribution of much of the erratic gravel is probably due 

 to agencies of earth-sculpture long anterior to the great Ice Age. 

 There remains one special piece of evidence adduced by Mr. 

 Lucy in favour of his contention, and this he considered of so 

 much importance that it formed the principal part of the sub- 

 ject of his annual address to the Field Club on quitting the 

 chair in 1893 {Proc. Cottes. Nat. Club, vol. cit., p. i). 



He there referred more especially to the discovery in the 

 Inferior Oolite, on Cleeve Cloud, of quartzose sand and of a 

 boulder of a similar character to some described in his previous 

 papers. The sand and the boulder, he says, belong to the 

 period of the great submergence. Similar sand also appears 

 in several places on the hillside. He had previously recorded 

 boulders of Carbonilerous Limestone, Millstone Grit, &c., in 

 the northern Cotteswolds, but not at so great an elevation. He 

 further proceeds to account for the absence of stride, and of the 

 fact that the Cotteswold rocks are not moutonn^e, on the sup- 

 position that the soft oolites would not retain striation, but 

 would be crushed by pressure. Consequently he claims the top 

 of Cleeve Cloud as a fine example of "glacial denudation," 

 whatever that may mean. The boulder from Cleeve Cloud is 

 now in the Gloucester Museum, and might well become a bone 

 of contention between the submerger and the glacialist as to 

 how it got into its elevated position of over looo feet. For- 

 tunately there is a third explanation, which, if it be correct, 

 shows how dangerous it is to build theories, as well as houses, 

 upon sand. Other distinguished members of the Cotteswold 

 Club are of opinion that the whitish sands on Cleeve Common 

 belong to the " Harford Sands," which constitute an integral 

 part of the Inferior Oolite itself. There may be some differ- 

 ence of opinion as to the concretionary nature of the boulders, 

 though these may well be nothing more than the " doggers," or 

 "pot-lids," so characteristic of calcareous sandstones. Mr. 

 Winwood believes that " the so-called foreign boulder" in the 

 Gloucester Museum evidently came from the " Harford Sands." 

 So far, therefore, the evidences of glacial action in the Cottes- 

 wolds do not rest on a very sure foundation. Yet the Severn 

 valley separates that range from an area on the west, where 

 there are clear evidences of local glaciation, as described in the 

 " Annual Report of the Geological Survey for 1896." Portions 

 of this material find their way into the river bed and elsewhere 

 as Drift which has most probably been rearranged — hence the 

 so-called Boulder-clay and Drift in the bed of the Severn. 

 Once more, then, in the cycle of geological time we perceive 

 that our district lies on the confines of two distinct sets of 

 phenomena. West of the Severn and north of the Bristol 

 Channel the evidences of considerable local glaciation are 

 obvious, whilst this can hardly be said of the Cotteswolds, the 

 Mendips, or the Quantocks. 



To the more recent geological history of our district it will 

 be sufficient to allude in the briefest terms, when I remind you 

 of the paper by Mr. Strahan on the deposits at Barry Dock, 

 and the still later one by Mr. Codrington on the submerged rock 

 valleys in South Wales, Devon, and Cornwall. Here we have 

 important testimony to certain moderate changes of level which 

 have taken place, and a picture is presented to us of the Bristol 

 Channel as a low-lying land surface, with streams meandering 

 through it. Thus a depression of something like 60 feet appears 

 to be the most recent change which the geologist has to record 

 in the estuary of the Severn. 



