NATURE 



roi 



THURSDAY, FEBRUARY 13, 1896. 



POPULAR GEOLOGY. 

 Open- Air Studies: an Introduction to Geology Out-of- 

 doors. With illustrations. By Prof. Grenville A. J. 

 Cole, M.R.I. A., F.G.S., &c. Pp. viii + 322. (London : 

 Griffin and Co., Limited, 1895.) 

 pROP\ GRENVILLE COLE has already won him- 

 •■- self wide repute as a writer on geological science 

 by his book, entitled "Aids in Practical Geology" 

 (Griffin and Co.). There Prof. Cole treated the branches 

 of mineralogy, petrology, and palaeontology, dwelling 

 more particularly on methods of work in laboratory and 

 museum. This recent publication, " Open-Air Studies," 

 breathes another atmosphere, lighter, gayer, and for the 

 popular mind more enticing. The Professor leads his 

 readers, like a class of students, into one countryside after 

 another, makes use in imagination of bicycle and railway 

 on the low ground, ascends boldly into glacier-swept 

 regions, and roams at will across moorland and highland 

 Everywhere he directs their powers of observation, 

 drills great facts into them by presenting particular 

 aspects again and again as occasion offers. Now and 

 then the Professor calls a halt to recapitulate, set in 

 order, or give more careful demonstration of strati- 

 graphical difficulties. 



The "Open-Air Studies" are ten in number. The 

 author gives the key-note in his preface : "In our 

 walks abroad we may be struck by this or that detail, 

 seemingly trivial in itself, which finally leads up to 

 some one of the vexed problems of the globe." The 

 first chapter gives some preliminary teaching on " The 

 Materials of the Earth," the rock-forming minerals 

 being carefully examined. It is not until chapter ii. 

 that the author takes his pen into the "Open Air." 

 We are told : " We must imagine that we wake up on a 

 fine clear morning at the foot of some of our wild moun- 

 tain-masses in the British Isles" (p. 28), and we are 

 guided up a swirling stream, past pools and waterfalls, 

 to " a mountain hollow." On our way, our professorial 

 guide bids us do many simple things. We have to "dig 

 for a little while with a walking-stick," that "we maybe 

 able to see the tiny streamlet flowing " ; we have to note 

 that the " loose blocks, half buried in the grass, are made 

 of the same materials as the cliffs " ; to watch how, if 

 some one kicks a stone, "it goes bounding down across 

 the grass, it leaps over one or two of the little cliffs, and 

 so descends until it rests on some lower ledge of the hill- 

 side " (p. 30). Then we put our fingers into pot-holes, 

 and move the pebbles in them, and we watch the stream 

 washing down its load of mud and pebble, and listen to 

 its rattling stones. 



In this manner the pleasant little object-lesson is con- 

 tinued, and the attentive follower is made to observe for 

 himself the forces of denudation at work on a mountain- 

 side. Arrived at the mountain-tarn, the Professor is 

 beguiled by the endless questions which rise to our lips 

 into delivering quite a learned lecture on nature's tools — 

 cloudland ; wind, dew, and rain ; frost, ice, and snow ; 

 stream, glacier, and avalanche. In the midst of it, we 

 NO. 1372, VOL. 53] 



find ourselves frequently transported to glaciated Alpine 

 valleys. Cirques are described and explained, an illustra- 

 tion is given of a snow-filled cirque on the Matterhorn, 

 and applied to the past history of our own mountain- 

 hollows. 



From the tenour of this chapter, which is a fair type, it 

 will be seen that Prof Cole limits the subject-matter of 

 his new book to that contained in any ordinary elementary 

 text-book of geology. Familiar truths are re-set, and any 

 claim to originality or success rests entirely upon the 

 workmanship and brilliancy of that re-setting. 



If we rightly understand Prof. Cole's method, it is the anti- 

 thesis of the analytic method practised bya text-book writer. 

 The latter passes, as it were, the diffuse light of know- 

 ledge through his own prism-acting mind, and it appears 

 on his manuscript as a fully-resolved spectrum in which 

 every band of colour is clearly presented to the student. 

 Prof. Cole's method, on the other hand, is to call upon 

 each student to make his own mind the prism. Observa- 

 tions, massed together with all the local details of nature, 

 are thrown upon the student's mind, which may or may 

 not be fit to act on its own account as a clear prism. 

 Theoretically the system is laudable, but decidedly un- 

 stable. The author himself succeeds in carrying it out 

 only through about one-half of the 313 pages of " Open- 

 Air Studies." Certainly half the chapters — i., vi., vii., viii., 

 and x. — are really text-book studies, and these are, more- 

 over, the most concise and complete in their treatment. 



To proceed with the actual contents, chap. iii. is called 

 " Down the Valley." Its central theme may be thus 

 expressed, in the words of the author : " The story of all 

 streams is alike — excavation at one end and deposition at 

 the other ; and the area of deposition extends slowly back 

 up the valley as time goes on " (p. 80). A typical Tyrolese 

 valley is made the main basis of observation. The 

 cutting of deep gorges by torrential side-streams, the 

 spreading-out of talus-cones at the mouth of tributary 

 valleys, the " creep " of a hillside downwards, landslips, 

 the occasional damming up of the stream and formation 

 of a lake, the resulting wide agricultural flats where 

 these become later silted up or drained — these and other 

 features are described with copious reference to famous 

 scenes and incidents in the Alps. 



The river Rhine is studied between Chur and the 

 Lake of Constance, to illustrate alluvial deposits and the 

 variations which take place in the course of a river. A 

 "delta" is defined, examples given, and brought home to 

 us by the remark that "an enterprising child with a 

 spade can soon produce a shallow lake, and can observe 

 how it becomes filled and obliterated by the encroach- 

 ment of a delta at its upper end " (p. 86). 



The main discussion of deltas, however, falls into the 

 following chapter, " Along the Shore." There, too, the 

 first lessons on sedimentary deposits are given. The 

 abrasion of a coast-line by the action of the waves, leads 

 up to an explanation of Sir Andrew Ramsay's term 

 " plain of marine denudation." The author then goes 

 on to show how the wom-away material is reconstructed 

 into different kinds of strata bedded beneath sea, lake, 

 and river. Even deep-sea deposits of sihceous organisms, 

 the growth of coral-reefs, and the formation of oolites 

 find a place here, although the chapter begins and ends 



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