Penny Blood: Serial Sensation and Working-Class Entertainment — page 148: what you’re looking at

Machine-transcribed from the original scan — historical spelling and the odd misread are preserved.

cH. x.] DISTURBED TRACT. 131 relative movement towards that region has occurred from the opposite sides. We will now attempt to trace the formation of an elevated region by the compression of a tract of crust. We suppose that the compression has thickened the tract by crushing and corrugating the rocks of which it 1s composed, and that this thickening is greater about that part of the tract which was first compressed, and gradually subsides towards the region or regions from which the movement came. We also conclude that there will be what we have called a neutral zone, or level within the crust, above which the material will on the average be sheared upwards, and below it downwards. It will corre- spond with the caoutchouc band in Professor Favre's experi- ments, ‘The position of the neutral zone will depend upon the law, according to which the plasticity of the material changes at different depths. We have however seen that its position below the surface lies probably at between } and 4 of the total thickness of the crust, and that this result, combined with our knowledge of the temperature at which granite has been formed, shows that the total thickness must exceed twenty-one miles, and that this conclusion agrees well with the fact that the melting tempera- ture of rock in the dry way may be expected to occur at a depth of less than about thirty miles. We will take therefore as the bases of our working hypo- thesis, that the undisturbed crust is about twenty-five miles thick, and that the neutral zone is at the depth of about ten miles from the upper and fifteen from the lower mean level. Consequently, where the tract 1s compressed, it is easily seen that the thicknesses of the elevated and depressed portions above and below the mean levels will be in the same ratio, viz, of 2: 3. Since the compression along the tract acts in a line which falls within the crust it will not have any tendency to open fissures, but on the contrary to prevent their being formed or to close them if they exist, so that the subjacent fluid will not as a rule gain access to, and overflow, the depressed parts = (b) of the upper surface. GONG oOo SS (CO)