Lyell.--In 1830 there was published an epoch-making work in geology by Charles Lyell (Fig. 97), afterward Sir Charles, one of the most brilliant geologists of all the world. This British leader of scientific thought showed the prevalence of a uniform law of development in reference to the earth's surface. He pointed out the fact that had been maintained by Hutton, that changes in the past were to be interpreted in the light of what is occurring in the present. By making a careful study of the work performed by the waters in cutting down the continents and in transferring the eroded material to other places, and distributing it in the form of deltas; by observing also the action of frost and wind and wave; by noting, furthermore, the conditions under which animals die and are subsequently covered up in the matrix of detritus--by all this he showed evidences of a series of slow, continuous changes that have occurred in the past and have molded the earth's crust into its present condition. [Illustration: Fig. 97.--Charles Lyell, 1797-1875.] He showed, further, that organic fossils are no exception to this law of uniform change. He pointed to the evidences that ages of time had been required for the formation of the rocks bearing fossils; and that the regular succession of animal forms indicates a continual process of development of animal life; and that the disappearance of some forms, that is, their becoming extinct, was not owing to sudden changes, but to gradual changes. When this view was accepted, it overthrew the theory of catastrophism and replaced it by one designated uniformatism, based on the prevalence of uniform natural laws. This new conception, with all of its logical inferences, was scouted by those of theological bias, but it won its way in the scientific world and became an important feature in preparing for the reception of Darwin's great book upon the descent of animal life. We step forward now to the year 1859, to consider the effect upon the science of palæontology of the publication of Darwin's _Origin of Species_. Its influence was tremendous. The geological theories that had provoked so much controversy were concerned not merely with the disappearance of organic forms, but also with the introduction of new species. The _Origin of Species_ made it clear that the only rational point of view in reference to fossil life was that it had been gradually developed, that it gave us a picture of the conditions of life upon the globe in past ages, that the succession of forms within the rocks represented in outline the successive steps in the formation of different kinds of animals and plants.