The Quarterly journal of the Geological Society of London . he differential movement to which the crush-conglomerates bear testimony has been the result of the differentdegrees of compressibility of which these two distinct types of rockare capable. On a small scale this difference is clearly illustratedin some of the sections above described, and its effect upon a broadscale must have been very considerable. If, under the influence of a powerful lateral thrust, the slateswere forced into narrower bounds than the same pressure was ableto induce in the grits, a partial rending asunder of the in
The Quarterly journal of the Geological Society of London . he differential movement to which the crush-conglomerates bear testimony has been the result of the differentdegrees of compressibility of which these two distinct types of rockare capable. On a small scale this difference is clearly illustratedin some of the sections above described, and its effect upon a broadscale must have been very considerable. If, under the influence of a powerful lateral thrust, the slateswere forced into narrower bounds than the same pressure was ableto induce in the grits, a partial rending asunder of the interlockedmasses and a shearing of the one over the other must have inevitablyfollowed. Under such conditions I imagine the crush-conglomeratesto have been produced, through the breaking-up of the passage-beds,as shown in the accompanying diagram (fig. 12). Except for the Fig. 12.—Diagram to illustrate the p>ossible result of strong lateralpressure upon a more compressible argillaceous series, restingon and passing into less compressible sanely a-a (between dotted lines) = space originally occupied by the gritty (between dotted lines) = space originally occupied by the argillaceous = Grits after compression. B-B = Slates after compression. 0. Zone of shearing and brecciation. Note.—The beds are supposed to be driven in from the side indicatedby the horizontal arrow. presence of these passage-beds, and the absence therefore of asharp line of demarcation, it is probable that the strain would havefound relief in the formation of a great thrust-plane, or a series ofsuch planes. Instead of this, the rending force was distributedthrough a large thickness of rock, which was thereby shattered. The occurrence of the conglomeratic structure at one side only ofthe stratigraphical axis is an important point which I shall notseek at present fully to discuss. It appears to indicate the existenceof some such definite relationship between the general structure o
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Keywords: ., bookcentury1800, bookdecade1840, bookidquarte, booksubjectgeology
