. Bulletin of the Geological Society of America. Geology. 254 B. WILLIS DISCOIDAL STRUCTURE OF THE LITHOSPHERE JJ m Before Compression made possible to ascertain the internal friction by subtracting the resist- ance of the steel cylinder from the total pressure. To apply these results to the case of the lithosphere, let us consider the pressure applied to the ends of the rock specimen as a tangential or hori- zontal stress, and conceive the resistance of the steel cylinder to be replaced by a vertical rock column which would exert the same pressure. Then, in order that the latter should be rai
. Bulletin of the Geological Society of America. Geology. 254 B. WILLIS DISCOIDAL STRUCTURE OF THE LITHOSPHERE JJ m Before Compression made possible to ascertain the internal friction by subtracting the resist- ance of the steel cylinder from the total pressure. To apply these results to the case of the lithosphere, let us consider the pressure applied to the ends of the rock specimen as a tangential or hori- zontal stress, and conceive the resistance of the steel cylinder to be replaced by a vertical rock column which would exert the same pressure. Then, in order that the latter should be raised in the manner and to the degree that the steel cylin- der was bulged, the differential horizontal stress must be sufficient to overcome, not only the weight of the rock column, but also the internal friction or flow-strength of the rock specimen. Adams used steel jackets having walls centimeter thick in one set of experiments, and in a sec- ond set centimeter thick. The former exerted a resistance of 36,685 pounds to the square inch, and was therefore equivalent to the load of miles of rock of specific gravity The steel cylinder, centimeter thick, resisted with a pressure equivalent to 37,359 pounds, or a load of miles of rock. The above values are those given by Adams for the stage of experiment ^Svhere the regular column shows a diametrical increase of inch (or per cent), that is, when the deformation is well under way, and after which it becomes proportional to the tangential pressure.'' Plotting the numerical results given by Adams for successive stages of the experi- ments on granite, one obtains curves which show very marked deforma- tion before the steel had developed a resistance equal to the values given above, and if one were looking for the precise point at which the rock began to flow, somewhat less depths than and miles would prob- ably be chosen; but I prefer to take the values deduced by Adams as representing a st
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