Another ingenious idea was suggested by the late Mr. Scrope, whose work on volcanoes is well known. His idea was that when a large amount of sedimentary material has accumulated on any large area of the bed of the ocean, it somewhat checks the flow of heat from within, and therefore the temperature of the rocks forming part of the earth's crust below will be increased, much in the same manner as a glove checks the escape of heat from the hand and keeps it warm. The consequence of this would be expansion; and as such expansion would be chiefly in a horizontal direction, the area would bulge upwards and cause elevation of the strata resting on it. But there are several difficulties which this theory fails to explain. And lastly, Professor Le Conte, holding that the contraction theory is unsatisfactory, accounts for earth-movements of all kinds by supposing that some internal parts of the earth cool and contract faster than others. Those parts that cool fastest, according to this theory, are those that underlie the oceanic basins or troughs; while the continental areas, not cooling so rapidly, are left standing up in relief. This theory, which does not seem very satisfactory, is based upon the idea that some parts of the earth's interior may be capable of conducting heat faster than others. We know that some substances, like iron, are good conductors of heat, while others are bad conductors; and it is therefore conceivable that heat may be flowing faster along some parts of the earth than along others; and if so, there would be differences in the rate of contraction.