It is a curious fact in the history of progress, that, by a kind of intuitive insight, the earlier observers seem to have had a wider, more comprehensive recognition of natural phenomena as a whole than their successors, who far excel them in their knowledge of special points, but often lose their grasp of broader relations in the more minute investigation of details.  When geologists first turned their attention to the physical history of the earth, they saw at once certain great features which they took to be the skeleton and basis of the whole structure.  They saw the great masses of granite forming the mountains and mountain-chains, with the stratified rocks resting against their slopes; and they assumed that granite was the first primary agent, and that all stratified rocks must be of a later formation.  Although this involved a partial error, as we shall see hereafter, when we trace the upheavals of granite even into comparatively modern periods, yet it held a great geological truth also; for, though granite formations are by no means limited to those early periods, they are nevertheless very characteristic of them, and are indeed the great foundation-stones on which the physical history of the globe is built.

Starting from this landmark, the earlier geologists divided the world’s history into three periods.  As the historian recognizes as distinct phases in the growth of the human race Ancient History, the Middle Ages, and Modern History, so they distinguished between what they called the Primary period, when, as they believed, no life stirred on the surface of the earth, the Secondary or middle period, when animals and plants were introduced and the land began to assume continental proportions, and the Tertiary period, or comparatively modern geological times, when the aspect of the earth as well as its inhabitants was approaching more nearly to the present condition of things.  But as their investigations proceeded, they found that every one of these great ages of the world’s history was divided into numerous lesser epochs, each of which had been characterized by a peculiar set of animals and plants, and had been closed by some great physical convulsion, that disturbed and displaced the materials accumulated during such a period of rest.  The further study of these subordinate periods showed that what had been called Primary formations, the volcanic or Plutonic rocks, formerly believed to be confined to the first geological ages, belonged to all the periods, successive eruptions having taken place at all times, pouring up through the accumulated deposits, penetrating and injecting their cracks, fissures, and inequalities, as well as throwing out large masses on the surface.  Up to our own day there has never been a period when such eruptions have not taken place, though they have been constantly diminishing in frequency and extent.  In consequence of this discovery, that rocks of igneous character were by no means exclusively characteristic of the