Oct 26, 1876] 



NATURE 



567 



and when the two thermometers read alike, the atmo- 

 sphere is exceedingly damp." 



This statement is not likely to give any very definite 

 idea of the conclusions which may be drawn from the 

 readings of the thermometers, and the difference may be 

 less at one time than another, and yet the air be " drier." 

 In cyclonic systems, the author says, " the air circulates 

 more rapidly [than in anti-cyclonic], causing strong 

 winds, and appears to flow in towards the centre, so that it 

 must naturally be supplied from below and ascend in the 

 centre." Here the rapid circulation of the air is said to 

 be the cause of the wind. It is also said elsewhere that 

 U is calm in the centre. Is it meant as a result of obser- 

 vation that the air flows towards the centre 1 and is it a 

 result of observation that the air (naturally or not) rises 

 in the centre ? 



We have already alluded to the little use of the tension 

 of vapour in " storm warnings." With reference to one 

 case, we find : " The absence of rain is very noticeable 

 during the early period of the gale ; the reason for this 

 absence can be seen from the fact of the great dis- 

 tance [on the curves given] between the wet and dry ther- 

 mometers." The difference is about 3° with the dry 

 thermometer near 50°, and the wind blew " pretty steadily 

 from S.S.W. for twenty hours " (p. 68). If the fact that it 

 did not rain was an unusual one under the circumstances, 

 and if that depended on the difference of the thermo- 

 meters, the question seems to us only changed to what 

 was the reason of the difference 1 



We do not always read the curves as the author has 

 done, nor always agree with his reasoning from them ; 

 and in some cases, as p. 72, where one cyclone has 

 passed eastwards, north of a station, leaving a N.W. 

 wind, and is followed by another also passing north, the 

 author has not made it very clear why the wind should 

 back to S.W., to S., and S.E., through the action of the 

 S.E. wind of the second cyclone meeting the N.W. of the 

 first. 



These queries and suggestions do not affect the general 

 character of the book, which we can recommend as a 

 useful and instructive companion in the study of weather 

 charts, and for the comprehension of storm-warnings as 

 they are issued from the Meteorological Office. It is 

 much to be desired for the many who will not read this 

 work, yet cast a curious eye on the isobars in the news- 

 papers, that some condensed statement of the general 

 rules should occasionally accompany them. 



John Allan Broun 



GEIKIE'S GEOLOGICAL MAP OF SCOTLAND 

 Geological Map of Scotland. By Archibald Geikie, 

 LL.D., F.R.S., Director of the Geological Survey of 

 Scotland ; Murchison Professor of Geology and Mine- 

 ralogy in the University of Edinburgh. (Edinburgh 

 and London : W. and A. K. Johnston, 1876.) 



SINCE the publication of the last edition of the sketch- 

 map by Sir R. I. Murchison and Prof. Geikie, no 

 general geological map of Scotland has, so far as we are 

 aware, been issued, while those older than the sketch-map 

 rather served as guides to localities where minerals and 

 rocks were to be found, than afforded any clue to the sub- 



divisions of geological time represented by our ancient 

 formations. During the last twelve years, however, mate- 

 rials have been accumulating which have daily rendered 

 the sketch-map more and more inadequate to the purposes 

 for which it was originally designed, and it had obviously 

 become necessary either to issue a new edition, or to 

 "reform it altogether." Considering all things, and espe- 

 cially that he could no longer avail himself of the co- 

 operation of his late colleague, Prof. Geikie has, wisely we 

 think, decided on the latter course. The comparatively 

 large scale adopted (ten miles to the inch), gives room for 

 a number of details which had to be omitted from previous 

 maps. 



The publication, for the greater part of the south ot 

 Scotland, of the Geological Survey Maps on the scale 

 of one-inch and six- inches, reduces to some extent the 

 operations of the compiler to the selection of as much of 

 the details as his map gives him room to insert. At the 

 same time there are many points regarding the relations 

 of distant deposits which can be better seen on reviewing 

 the work as a whole than during the progress of detailed 

 mapping, and on some of these, as we shall presently 

 point out, Prof Geikie takes up an independent position. 

 The northern half of Scotland is in a very different 

 state as regards our knowledge of its geology. Here and 

 there, it is true, competent observers have selected choice 

 bits, and have worked them out with a thoroughness that 

 leaves little to be desired. But a great part of the High- 

 lands is still unknown to geologists, or only known in so 

 far as concerns its comparatively simple glacial pheno- 

 mena. For this region we have to consult ** geognostic 

 travels" of the beginning of the century, and put the best 

 construction on them that we can. It is not, therefore, 

 to be wondered at that this portion of the map is some- 

 what vague. The metamorphic rocks of the Highlands 

 offer difficult problems to the chemist and physicist, as 

 well as to the geologist ; and whoever attempts to unravel 

 their structure as a whole, must probably be content to 

 work for some years in the dark, and with the conscious- 

 ness that he may not see the issue of his own labours. 



Till recently the Southern Uplands were pretty much 

 in the same state as the Highlands, but the detailed work 

 of the geological survey, and a few private observers, has 

 filled up this great blank and rendered possible a com- 

 parison of the structure of the Silurian rocks there with 

 those of England and Ireland. On the map now before 

 us, are laid down, for the first time, all the more im- 

 portant graptolite bands which for a hundred miles, at 

 least, appear at intervals among the upturned Lower 

 Silurian strata between the Rhinns of Galloway and the 

 Tweed, while a marginal section explains how the Llan- 

 deilo beds, after folding over and over, are unconform- 

 ably succeeded near the northern edge of the uplands by 

 Caradoc basins, and on the south by rocks supposed to 

 be Upper Silurian. It thus appears that on the southern 

 side of Murchison's " axial beds " only a small part of 

 the northern series is repeated, the place of the Moffat 

 shales not being reached at the point where the Upper 

 Silurian rocks begin. 



North of the Uplands a notable feature of the new map 

 is the rearrangement of the Old Red and Carboniferous 

 boundary-line. The identity of the bright-red, sharp, 

 siliceous sandstones below the cement-stone series of the 



