Page:Geology and Mineralogy considered with reference to Natural Theology, 1837, volume 1.djvu/44

 40 transition, secondary, and tertiary series, more from a sense of the convenience of this long received arrangement, than from the reality of any strongly defined boundaries by which the strata, on the confines of each series, are separated from one another.

As the materials of stratified rocks are in great degree derived, directly or indirectly, from those which are unstratified, it will be premature to enter upon the consideration of derivative strata, until we have considered briefly the history of the primitive formations. We therefore commence our inquiry at that most ancient period, when there is much evidence to render it probable that the entire materials of the globe were in a fluid state, and that the cause of this fluidity was heats The form of the earth being that of an oblate spheroid, compressed at the poles, and enlarged at the equator, is that which a fluid mass would assume from revolution round its axis. The further fact, that the shortest diameter coincides with the existing axis of rotation, shows that this axis has been the same ever since the crust of the earth attained its present solid form.

Assuming that the whole materials of the globe may have