Oct. 1 8, 1883] 



NA TURE 



587 



LETTERS TO THE EDITOR 

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"Elevation and Subsidence" 



I have only to-day found time to read Mr. Starkie Gardner's 

 essay on "Elevation and Subsidence"; in the last paragraph 

 Mr. Gardner states that the views he advances are not accepted 

 by all geologists. As one who is entirely opposed lo them, will you 

 allow me to state as briefly as possible on what grounds I object 

 to the theory he propounds, and how I account for the observed 

 facts he mentions in support of it. 



It is generally admitted that nearly the whole of the sedimentary 

 rocks were depo-ited in shallow water and in si iwly subsiding 

 areas ; no one who has examined the Cambrian deposits of the 

 Longmynd or the Silurian deposit- of the Ingle 1 orough district, 

 will dispute this assertion. Mr. C. E. Dutton, in his recently 

 published monograph of the survey of the Grand Canon district 

 states, "Throughout the entire Plateau Province the strata are 

 shallow water deposits." 



That in areas so widely separated the same phenomena should 

 occur must necessarily suggest that similar processes of sub- 

 sidence and deposition were taking place. The sea-bottom in 

 these areas was, I believe, subsiding, not as Mr. Gardner 

 suggests " pari passu" with the deposition and in consequence 

 of it, but at a slower rate than that of the deposition, as the 

 result of forces actuating the crust of the earth, which are quite 

 independent of either deposition or denudation. 



The result of a slow subsidence and a more rapid deposition 

 would be that in course of time the surface of the deposited 

 matter would rise above low-water level and would be subjected 

 to the levelling or denuding action of the tides, any accumula- 

 tion of deposited matter above this level would be swept into 

 deeper water, all the phenomena of ripple marks, sun-cracked 

 surfaces, and worm trails would occur, and any tendency of the 

 slow rate of the subsidence t} lower the surface receiving the 

 deposited matter would necessarily be continually neutralised 

 by fresh accumulations. 



The areas of subsidence would probably present the appear- 

 ance of the large stretches of sand-banks which may be seen at 

 the mouths of the Mersey and of most of our rivers ; the e 

 banks are exposed at low and covered at high water. 



The accumulation of strata would continue as long as the sub- 

 sidence took place (providing material were brought down to 

 the sea) ; if the subsidence ceased, the material resulting from 

 denudation would be spread over a larger area, but no addi- 

 tional thickness or strata could be formed above the level just 

 mentioned ; on the other hand, if the deposition ceased and the 

 subsidence continued, an area of deep sea would be formed, and 

 probably a stratum of limestone would be accumulated. 



Further, the elevation of areas over which large accumulations 

 of matter have been deposited cannot have taken place in conse- 

 quence of denudation resulting in a greatly reduced weight 

 being distributed over the area of elevation, as suggested by Mr. 

 Gardner, for denudation has necessarily followed elevation. 



Every formation appears to me to contain evidence that sub- 

 sidence took place independently of deposition, and elevation 

 independently of denudation. 



The Cambrian and Silurian rocks in this country appear to 

 have been deposited over areas in which the rate of subsidence 

 has at one time been less, at another time greater, than the rate 

 of deposition ; the Silurian limestones no doubt represent periods 

 of subsidence during which no deposition of denuded matter 

 took place. At the close of the Silurian era an upheaval must 

 have occurred, the result of forces powerful enough to overcome 

 the weight of both the Cambrian and Silurian formations, which 

 appear to have been thrown into a series of vast anticlinal 

 and synclinal curves. In the Longmynd district and near Ingleton 

 the strata are either vertical or inclined at a great angle. 



One result of this upheaval would be the formation of com- 

 paratively shallow lakes or inland seas, in which the Old 

 Red Sandstone would be deposited ; another would be the 

 formation of a land surface of Silurian rocks which would be 

 subjected to subaerial denudation. 



According to Mr. Gardner's theory (in support of which he 

 refers to the Himalayan range), the' elevation of the Silurian 

 rocks should have been continuous, for denudation would affect 

 them in the same manner as it is said to affect that great range, 

 and possibly the accumulating Old Red Sandstone would react 

 on the Silurian land surface as Mr. Gardner suggests the sub- 

 ae:ial deposits of the sub-Himalayan range react on the main 

 mountain chain. 



Instead, however, of the continued upheaval which theoretic- 

 ally should have taken place, a subsidence of the denuded 

 Silurian rocks commenced apparently over a very large portion 

 of this country, resulting in the formation of a deep sea in which 

 the limestone, the base of the Carboniferous series, was deposited, 

 in Derbyshire to a depth of nearly 5000 feet. Did this vast 

 accumulation of limestone cause a further subsidence ? No, the 

 forces actuating the crust of the earth were in no respect inter- 

 fered with ; a period of elevation must have followed, and a com- 

 paratively shallow sea was filled up with the Yoredale shales and 

 millstone grits, and a land surface formed represented by the 

 lowest coal seam — a coal seam that may be measured by inches, 

 nevertheless it was followed by a subsidence. 



Surely the force producing this subsidence was as independent 

 of the coal seam as that producing the previous upheaval was 

 independent of the limestone. 



Throughout the whole series of the coal measure; compara- 

 tively thin accumulations of coal, representing periods of rest or 

 perhaps slow elevation, were followed by prolonged periods of 

 subsidence. 



I do not think the depressed areas bounded by vertical cliffs 

 seen by Mr. Gardner in Iceland at all help his theory ; they are 

 just the phenomena one would expect to find in a highly volcanic 

 district ; on a very small scale they may be seen in any district 

 from under which material has been removed. 



T. Sington 



Grove Terrace, Kersal Moor, Manchester, September 22 



I fear readers of Nature must be weary and the courtesy 

 of the Editor taxed by the demands on its space. Moreover but 

 little actually new information has been elicited, though thanks 

 are due to the Rev. Osmond Fisher and Dr. Ricketts especially 

 for their contributions. 



That depression of the earth's crust fjllows on the addition of 

 weight and elevation ensues on its removal are facts that can no 

 longer be disputed or explained away. Those gentlemen, how- 

 ever, who object that the cause and effect do not follow each other 

 foot by foot are a little unreasonable, for resistance more or less 

 stubborn must be encountered, which may check the process for 

 a space, and then by yielding at last considerably accelerate it. 

 Those again who will see nothing in the array of facts beyond 

 fortuitous connection must be allowed to hold their opinion. 



The matter rests thus:- -The observations of many authors 

 have induced a belief that sedimentation causes subsidence, 

 through the increase of weight acting on and displacing a viscid 

 layer underlying the solid crust. If this is so, the displaced 

 matter must find room elsewhere, and it is only reasonable to 

 suppose that a slight elevation or bulging of the crust must result 

 in more or less adjoining areas, and chiefly under areas in which 

 denudation had already weakened the resisting power by re- 

 ducing the pressure. Applying the idea to coasts, where v e 

 have for the most part parallel lines of denudation by wave 

 action and sedimentation through the deposition of material 

 dislodged by the waves, I have endeavoured to show that their 

 chief physical features accord with the "elevation and sub- 

 sidence" theory, though more observations are greatly to be 

 desired. But, even including coast lines, the examples are so far 

 but local manifestations, yet, if true in less matters, why not in 

 greater? Oceanic basin*, if permanent throughout geological 

 ages, as they probably have been, must have been areas of 

 sedimentation on a stupendous scale, and the pressure they 

 exert (increased as subsidence deepens the column of water) 

 must give rise to corresponding displacements on a gigantic scalei 

 and which would seek relief along the nearest existing lines of 

 weakness. These lines would either be in the ocean and result 

 in banks or ridges, or else be along their margins and result in 

 mountain chains, and sometimes breaking through in volcanic 

 outbursts. The larger would overcome the smaller, and a delta 

 or coast line subsiding through its own sedimentation might 

 occur along the line of upheaval and be forced upward, or a 

 vast displacement or eruption might relieve the tension to an 

 extent that would take ages of accumulation to reproduce. This 



