May 31, 1883] 



NA TURE 



99 



THE GEOLOGICAL HISTORY OF BRITAIN 



Contributions to the Physical History of the British Isles ; 

 with a Dissertation on the Origin of Western Europe 

 and of the Atlantic Ocean. Illustrated by 27 Coloured 

 Maps. By Edward Hull, F.R.S., &c. (London: 

 Stanford, 1882.) 



IF Geology may be correctly described as a history of 

 the earth, then a geologist is in the first place and 

 essentially a historian. His function is to trace back the 

 gradual growth of the world, organic as well as inorganic, 

 and to show through what successive stages the present 

 conditions of geography and of life have been reached. 

 His materials, like those of the historian of human pro- 

 gress, become fewer and less reliable in proportion to 

 their antiquity. More and more as he pilots his way into 

 the records of the remoter past is he driven to piece 

 together their evidence with conjecture, until at last 

 evidence of every kind fails him, and he is reduced to 

 mere speculation. There is undoubtedly a strong tempta- 

 tion to minds of a particular order to indulge in wide 

 excursions into the unknown realms of primeval cos- 

 mogony. The fewer the facts that may serve as guide- 

 posts the greater the scope for the fancy. So long as the 

 picture does not appear to outrage our established con- 

 ceptions of physical law its enthusiastic limner considers 

 himself within the safe limits of fact or, at least, of legiti- 

 mate inference. He does not stop to consider whether 

 his restoration may not in itself be flagrantly improbable, 

 or whether enough may not be already known on the sub- 

 ject to show that it is quite untenable. In this way much 

 harm has been done to the progress of sound geology. 



The attempt to restore former aspects of the globe, or 

 at least of different areas of its surface, may be made with 

 fair measure of success up to a certain point. As the 

 geologist goes beyond that point he leans more and more 

 on conjecture. It is very desirable, for his own sake as 

 well as for that of the subject, that the actual data on 

 which he proceeds should be definitely stated. His 

 readers ought to know exactly where ascertained fact 

 ends and restoration begins. Yet he may be so con- 

 vinced of the truth of his restoration that, until challenged 

 to set down in definite form the amount of evidence 

 actually at his command, he may honestly have come to 

 regard some of his deductions as well-established truths. 

 He cannot, however, be too careful to draw a clear and 

 sharp line between what he knows and what he infers, 

 when it is his object to write geological history. 



One of the most attractive branches of this history is 

 that which deals with the gradual growth of a country or 

 continent. Many interesting and important memoirs on 

 this subject have appeared, more especially in England 

 where it has long been a favourite study. Sketch-maps 

 have been published indicating in a somewhat vague way 

 what the authors believe to have been the probable dis- 

 tribution of sea and land at former geological periods. 

 Among those who by their original researches have contri- 

 buted materials towards the restoration of ancient geogra- 

 phical conditions in Britain, Prof. Hull, the Director of 

 the Iriih Geological Survey, deserves honourable mention. 

 His papers upon the changes that occurred during Car- 

 boniferous, Permian, and Triassic times, and upon the 

 south-eastward attenuation of the Jurassic series in this 



country are well known to geologists. He has now, how- 

 ever, attempted a much more ambitious task than any 

 one has yet ventured upon in this department of science. 

 He has published a series of maps representing what he 

 conceives to have been the successive geographical phases 

 through which the region of the British Islands has 

 passed from the earliest geological times. Without dis- 

 cussing the question whether the information at the 

 disposal of geologists is yet sufficiently ample and precise 

 to warrant an attempt of this kind, one may at least 

 demand that every care should have been taken to show 

 precisely what is actually known fact and what is inference. 

 But Mr. Hull gives us scanty guidance in this respect. 

 There is not one of his restorations that does not prompt 

 the question on what grounds its details have been put 

 together. The position of former areas of sea is usually 

 sufficiently definable, but it is by no means so easy to 

 say what was land, and still more difficult to assign even 

 the most conjectural outlines to the shores. The author 

 doubtless thinks his geographical boundaries vague 

 enough ; we are inclined to regard them as a good deal 

 more definite than the actual evidence in many cases 

 warrants. To take as an illustration his map of Britain 

 during the Upper Silurian and what he terms the 

 " Devono-Silurian " periods ; we should like to know on 

 what grounds he makes Wales, the Lake Country, the 

 north-west of Ireland, and much of the Highlands of 

 Scotland elevated land at that time. The evidence, so 

 far as we are aware, is rather in favour of these areas 

 having been under the Upper Silurian sea ; at least we know 

 of no proof that they formed high lands, even after the 

 plication and metamorphism he refers to. Nor is there 

 any information as to why the author marks the area 

 from the mouth of the Humber to the middle of Norfolk 

 as part of his continental land. He mixes up in a 

 curiously unintelligible way his " Devono-Silurian " and 

 Lower and Middle Devonian formations, some of the 

 estuaries or lacustrine areas being placed with the older 

 group of strata, others with the younger, in accordance 

 with certain theoretical ideas which he has already 

 published. 



According to Prof. Hull's maps, most of the high 

 grounds of Britain have been elevated dry land since 

 the Lower Silurian period. No one, however, who has 

 seriously studied how the land is continuously denuded, can 

 believe this representation to be even approximately true. 

 Our mountains must have been many times, and probably 

 for long intervals, under water. Even if no large amount 

 of sedimentary material were laid down upon them, their 

 submergence would at least protect them from the degra- 

 dation which would otherwise have worn them down. 

 How does Prof. Hull know that Ireland, which was 

 almost if not entirely under water during the Carboni- 

 ferous period, did not remain more or less in the same 

 condition through several succeeding ages ? The presence 

 of Permian and Triassic deposits in the north-east of the 

 island shows that considerable denudation of the Car- 

 boniferous rocks had taken place there before these red 

 strata were laid down. But surely it is rather a large 

 inference from these slender data that all the rest of the 

 country was land, with high grounds where we see them 

 still. How can he tell that Ireland was not entirely 

 submerged beneath the Jurassic sea? Had it not been 



