would confine the origin of all seismical and volcanic disturbances and their consequent Geographical changes, to a mere shell of the crust.[1] The result of the computation is certainly interesting and we may hope will not be lost sight of in future discussions, however it may share in gaining support or opposition. It is based upon an assumption of the temperature when the earth began to cool, to assume a lower temperature draws the belt nearer to the surface and a higher temperature is believed to be inconsistent with our knowledge of what heat may effect. This belt is stated to be gradually sinking, however, and the computation, therefore, involves a term representing time, and I venture to suggest as estimates of Geologic time are generally indefinite and seem to be inexhaustible, an abundance can probably be supplied to sink the belt deep enough for all theoretical purposes.
More interesting to Geographers are the conceptions of ancient forms suggested by the views recently advanced by Prof. Shaler in a late number of Science (June 15, 1888), on "The Crenitic Hypothesis and Mountain Building." To let the imagination have full play, we may conceive that where we now have extensive mountain ranges, there were formerly great plains of sedimentation, and where we see the process of sedimentation active to-day there may be great mountains in the future. And also in his inquiry into the "Origin of the divisions between the layers of stratified rocks" (Proced. Boston Soc. Nat. Hist., vol. xxiii), we may be carried away with the immensity of the changes suggested. The recurring destruction of submarine life to contribute in the building of the rocks of the Continents: the apparently endless cycles of emergence of the land and subsidence of the waters, to leave the Geographical conditions we see to-day, furnish additional evidence of the wonders of the past and force upon us anew the realization of how little in the great evolution is the epoch in which we live.
American Geologists have advanced the knowledge of the world; only recently the American methods of Glacial study have enabled Salisbury to interpret the terminal moraines of Northern Germany (Am. Jour. Science, May, 1888), and that the Science is active among our countrymen is evidenced by the formation of a Geological Society and the establishment of a magazine de-
- ↑ In the American Geologist for February, 1888, Prof. Reade protests against the construction of the theory of a "belt or level of no strain" placing the foci of earthquakes and other disturbances in the strata above the belt.
