472 



NATURE 



[Sept. 28, 1876 



represent a district free from superficial accumulations, 

 and in which numerous alternations of hard and soft beds 

 afford the greatest facilities in detecting every deviation 

 of the strata from their normal position, the minute struc- 

 ture of the country will be found delineated in the most 

 exquisite detail ; while in an adjoining sheet broad spreads 

 of colour separated by dotted lines constitute a confession 

 that the surveyor was here engaged in an almost hopeless 

 task. It may, indeed, be questioned whether on a map 

 of so large a scale as that of the Geological Survey, any 

 useful purpose is answered by attempts to define the 

 boundaries of formations buried under several hundreds 

 of feet of boulder- clay or gravel. Another serious obstacle 

 to the perfecting of our geological maps is found in the 

 circumstance that rocks of identical mineralogical com- 

 position, but of very different geological age, are found 

 occasionally in direct apposition ; and in such cases 

 (except in the rare instances of numerous sections afford- 

 ing fossils characteristic of either formation presenting 

 themselves) the field-geologist finds himself hopelessly at 

 fault. For example, in those parts of England in which 

 the limestones and grits of the Coralline Oolite are found 

 intervening between the Oxford and Kimmeridge clays 

 the work of the surveyor is an easy one ; but where, 

 as is frequently the case, the first-mentioned formation is 

 absent and the one series of argillaceous strata lies directly 

 upon the other, the result attained by him is necessarily 

 of the most vague and uncertain character. On the 

 other hand, many of the hard and well marked rock- 

 masses, which the geological surveyor naturally seizes 

 upon in drawing his hnes of boundary, are too frequently, 

 alas, shown by the palecontologist to be altogether desti- 

 tute of any important significance. 



In spite, however, of these unavoidable inequalities and 

 imperfections in its execution, the map of the Geological 

 Survey is a splendid work, and one of which the country 

 may justly be proud ; it has already largely prevented the 

 wasteful expenditure of the resources of the empire in 

 futile undertakings, while it has brought to light many 

 unsuspected sources of mineral wealth ; and it is hard 

 to say whether in the future the aid which it will render 

 to those engaged in scientific research will not outrival 

 that which it now affords to industrial enterprise. 



The methods pursued by the Geological Survey of this 

 country, in seeking to realise that ideal to which we have 

 adverted, have been gradually developed in the hands of the 

 numerous able observers and sagacious thinkers, who have 

 since its foundation been members of its staff. Hitherto, 

 however, these methods have been handed down by tra- 

 dition only, and no work has existed to which an outsider 

 or foreigner could refer for an exposition and illustration 

 of them, Hence we gladly hail the appearance of the 

 present work, as satisfying a want which has long been 

 felt and frequently expressed. 



In the execution of his task we consider that the 

 author has been on the whole very successful, especially 

 when we remember that the experiment is the first of its 

 kind. His explanations are strikingly clear, simple, and 

 full ; indeed, we may perhaps suggest that some of the 

 mmute details into which he enters are unnecessary for 

 the class of persons to whom alone the book is likely to 

 be of service— those, namely, who have mastered the 

 elementary principles of geological science. For ex- 



ample, we think that the author might fairly have given 

 his readers credit for sufficient knowledge of plane tri- 

 gonometry to have enabled them to make use of a very 

 simple formula ; and he should therefore, it seems to us, 

 have substituted such a formula, with a table of tangents, 

 for the rule-of-thumb and. not very accurate methods for 

 calculating true from apparent dips, given in pp. 42-46. 

 His very minute directions, too, concerning the method 

 of running levels for the purpose of preparing geological 

 sections are, we think, a little out of place here, as they 

 differ in no respect from those in ordinary use among 

 engineers and surveyors, and may be found described in any 

 treatise on land-surveying. On the other hand, his sugges- 

 tions as to the use of two aneroids, one to be examined every 

 half hour at a fixed station, though correct enough in 

 theory, with other less exact 'methods applied to running 

 lines of level, are certainly likely to be of little actual 

 value to the geologist ; while there is an omission of any 

 reference to the really practicable applications of a single 

 aneroid, when used with Airy's tables, either for calcu- 

 lating approximately the difference of level between 

 two points {e.g., the height of a bed of gravel above 

 the level of the present stream), or in supplementing 

 the data found on a contoured map ; neither does our 

 author refer to the use of Abney's level and several other 

 simple contrivances which will be found very useful for 

 the same purpose. 



The sections on " Lithology " and " Pateontology " are 

 treated with less diffuseness than those on the preparation 

 of geological maps and sections. In a work of reference 

 like the present we cannot but regard the reduction of 

 the information to a tabular form, wherever this is prac- 

 ticable, as a great convenience ; and we commend the 

 adoption of the method in this part of the work. Mr. 

 Jukes-Browne's remarks on the collection, preservation, 

 and determination of fossils are, if not exhaustive, at least 

 very useful and practical ; but we can only consider the 

 index of characteristic fossils, as unnecessarily increasing 

 the bulk of the book, for no geologist who is able to 

 determine the species of a fossil is likely to be at any loss 

 as to the geological horizon to which it belongs. 



Geological surveying is an art which for its successful 

 performance requires some natural aptitude, a consider- 

 able knowledge of the principles and results of geological 

 science, careful training, and much practice. The perusal 

 of Mr. Penning's valuable hand-book will not make a 

 man a geological surveyor, but it may enable him to 

 appreciate some of the methods employed in the work — 

 at least under its simplest conditions — as carried out by 

 our national survey. And he who has mastered these 

 first principles as here set forth will be the better pre- 

 pared to encounter the more difficult problems which 

 are presented by areas of more complicated geological 

 structure and provided with less perfect topographical 

 maps than our own. J. W. J. 



THE BATS OF ASIA 



Monograph of the Asiatic Chiropiera. By G. E. Dobson, 

 M.A., M.B. (Printed by order of the Trustees of the 

 Indian Museum, 1 876.) 



BIOLOGISTS have, during the last few years, learnt 

 with interest many of the valuable facts brought 

 forward by Mr, Dobson, of Netley, with reference to the 



