54Q 



NA TURE 



[Oct. 4, 1883 



clay, that is of the urad, &c, which then issued in streams from 

 beneath the glaciers, and contains the pebbles derived from 

 it localities which had drifted in icebergs and coast-ice, 

 and been dropped into it, the land being raised l >a considerable 

 extent when, upon the return of a more genial climate, it was 

 relieved of its load of ice and snow. 



Prof. N. S. Shaler, of Harvard College, U.S.A., in 1874 

 (Mem. Boston Soc. Nat. Hist. vol. ii.), considering that by the 

 hypothesis of Adhemar the conditions which would have resulted 

 were not fulfilled during the last Glacial period, concluded that 

 we may more reasonably look to the weight of ice then accumu- 

 lated on the continents for the depression of the land areas it 

 occupied. 



In a paper on the "Cause of the Glacial Period," read before 

 Section C at the meeting of the British Association at Bristol, 

 1875 (Report, p. 79; also Geol. Mag., Decade II., vol. ii.) 

 I a Iduced evidence tending to prove that such a subsidence 

 of the Isthmus of Panama has taken place as would allow a 

 diversion of the equatorial waters of the Atlantic into the 

 Pacific ; as a consequence of which similar effects to those which 

 occurred during the Glacial period might have been produced. 

 The formation of the Canal ought to afford to competent ob- 

 servers absolute proof whether such has been the case or not. 

 In the course of the essay I ascribed not only the subsidence 

 during the Glacial period, hut also that now rapidly progressing 

 in Greenland, to the weight of the greatly increased accumulation 

 of snow ; and that the use of the land in Norway is dependent 

 on the removal of pressure by the melting or diminution of the 

 glaciers. It does not appear unlikely that to a great extent the 

 rising of the Andes may be due to the dissolution of the snow 

 which once covered these mountains in a greatly increased 

 degree, it may hive been contemporaneously with the Glacial 

 period in Europe and North America ; and in part to the 

 transfer of pressure, by the materials derived from its flanks and 

 brought down by the Amazon and its tributaries forming at its 

 delta the "measures" in this great oal-field of South America 

 n ow in process of formation. 



Mr. J. Slarkie Gardner, at a much later period (Geol. Mag., 

 June, 1S81) stated that great accumulations of ice in the Glacial 

 period seem to have been accompanied by subsidence, and even 

 Greenland at the present day may be sinking under its ice-cap. 

 In the same year the Rev. O. Fisher, in " Physics of the Earth's 

 Crust" (p. 223), accounted for the raised shell beds found in 

 Scandinavia at an altitude of 700 feet, by the country having 

 been formerly depressed owing toils being loaded with heavy 

 ice fields, and that its gradual subsequent rise may have been 

 caused by the ice having melted off. He remarks that similar 

 movements have occurred and are now going on in Greenland ; 

 and that the subsidence of 6 or 8 feet in a century may possibly 

 be accounted for by the snow-fall being at present greater than 

 ried olT by the glaciers and evaporation. 

 During the present yeor Mr. W. F. Stanley (Nature, vol. xxvii. 

 p. 523) held that the cause of the coast of Greenlaud sinking is 

 the weight of the present accumulation of ice upon that con- 

 tinent. Quite recently Mr. Searles V. Wojd (Geol. Mag., July, 

 18S3, footnote) thinks that the overwhelming of reindeer pas- 

 tures by the ice during the centuries of Danish occupation, and 

 the indicati ons of subsidence afforded by the position of ancient 

 dwellings, may show that the ice is now augmenting, and the 

 land sinking under its weight. 



But the great question is not to whom belongs the priority of 

 attributing the depression of the land during the Glacial period, 

 and at present in Greenland, to the weight of accumulated snow, 

 and the reelevation to its removal ; even this explanation of the 

 phenomena under consideration, important though it may be, is 

 but an item in the still greater one, namely, whether the depres- 

 sion which has taken place and is still in progress at the mouths 

 of great rivers, in their deltas, in the estuaries and bays into 

 which, emptying themselves, they carry mud, sand, pebbles, and 

 other debris, is caused by the weight of these accumulated 

 deposits pressing down the crust of the earth beneath them, thus 

 permitting further accumulation to any extent ; and also whether 

 the subsidence, which by every one is conceded to have occurred 

 during the deposition of all stratified rocks, from the earliest of 

 which we can read the record in the " great stone book " to 

 those now in progress, is due to the same cause — the weight of 

 the materials of which they have been formed. 



The converse has also to be inquired into, whether the eleva- 

 tion of the land and the formation of hills and mountains is the 

 result of the abrasion of the land and the transfer of the disin- 

 tegrated materials to a distance by rain and rivers ; thus reliev- 



ing by so much the locality from which they have been removed 

 of the weight pressing on the crust of the earth. The highest 

 hills in a district are those from which the greatest amount has 

 been removed by denudation, their summits not unfrequently 

 consisting of the lowest rocks in the geological series of the 

 neighbourhood. 



Birkenhead, September 22 Charles Ricketts 



I quite agree with Mr. Mackie in believing that "the con- 

 nection between sedimentation and subsidence on the one hand, 

 and between denudation and elevation on the other," are 

 "simply concomitant effects of the same cause ;" that, in fact, 

 depressions in the earth's crust are the cause of sedimentary 

 deposits, and not the deposits the cause of the depressions, and, 

 further, that the elevations and depressions are caused by lateral 

 pressure developed by the shrinking of the earth's crust ; but is 

 it necessary that certain parts of a depressed area should be 

 "strengthened by volcanic outbursts, &c, " ? I do not think 

 so. 



If a magazine or book with a paper cover be held close, and 

 pressed from back to front, the mass of the leaves is thrown into 

 anticlinal and synclinal curves though the book is at no point 

 stronger than at any other ; the pressure is broaght to bear up on 

 the book, and as it cannot " telescope," it is necessarily bent 

 upwards and downwards. Is this not something like what hap- 

 pens to the rock ? 



Take, for example, the Old Red Sandstone between the base 

 of the Grampians and the Carboniferous rocks of Fife. This is 

 a plain partly composed of sandstones, partly of sandstone with 

 interbedded volcanic rocks, and partly of solid masses of vol- 

 canic ejecta. The plain has been bent into two anticlinal and 

 two synclinal curves. 



In such a varied area, if anywhere, one would expect to find 

 evidence of the influence of the relative strength of the rocks in 

 m idifying their curvature. 



The syncline nearest to the Grampians is mainly composed of 

 sandstone and conglomerates ; as these rocks bend up towards 

 the anticlinal axis to the south, the Sidlaw Hills (composed of 

 hard sandstones and interbedded parphyrite, &c.) present a very 

 striking eximple of strengthening of the beds ; still they are 

 neither on the anticlinal nor the synclinal axis, for though near 

 to and towering high above the former, they lie on the slope of 

 the beds dipping towards the north. The rocks of the second 

 syncline are sandstones with intrusive and interbedded lavas, the 

 volcanic rocks greatly increasing in proportion to the sedimentary 

 towards the synclinal axis near the estuary of the Tay, towards 

 which the rocks are gently bent up, while across the estuary, 

 which occupies the position of the denuded arch of the anticline, 

 the rocks are almost entirely sheets of lava, with volcanic 

 breccias, &c. 



Thus we have a synclinal and anticlinal curve, both of sand- 

 stone, while the hard and thickly-bedded volcanic rocks form 

 part of the slope between them, and again we have a syncline 

 partly composed of interbedded lavas and sandstones, while the 

 almost entirely volcanic rocks are bent up into an anticline. 



It would therefore seem that the quality and thickness of the 

 rock masses have very little influence upon the form of the 

 curves into which they are bent. Jas. Durham 



Newport, Fife 



Photography and Still Life 



1 have been assured, by a gentleman to whose opinion all 

 dabblers in science photography must bow, that the following 

 method of photographing objects of still life was unknown to 

 him, and that its publication might prove useful to others. 



Having some years ago to photograph a series of implements 

 to illu-trate a paper on the Borness Cave, I was met at the out- 

 set by the difficulty of avoiding cast shadows and such acces- 

 sories as were needful for posing the objects to be copied. It 

 occurred to me that a pane of glass, a white cloth, and some 

 beeswax would meet the difficulty ; as objects fixed to the glass 

 by beeswax with a white cloth behind them would " come out " 

 on a white ground free from the shadows and accessories I 

 wished to avoid. Having been recently asked to photograph 

 some important bones, teeth, and flint implements, necessity, 

 "the mother of invention," has much improved on the original 

 rough process, and I can confidently recommend the following 

 cheap apparatus as extremely efficient, viz., a square pane of 

 plate glass with a hole drilled in the centre (for fastening such 



