Huxley.--Thomas Henry Huxley (1825-1895) was led to study fossil life on an extended scale, and he shed light in this province as in others upon which he touched. With critical analysis and impartial mind he applied the principles of evolution to the study of fossil remains. His first conclusion was that the evidence of evolution derived from palæontology was negative, but with the advances in discovery he grew gradually to recognize that palæontologists, in bringing to light complete evolutionary series, had supplied some of the strongest supporting evidence of organic evolution. By many geologists fossils have been used as time-markers for the determination of the age of various deposits; but, with Huxley, the study of them was always biological. It is to the latter point of view that palæontology owes its great importance and its great development. The statement of Huxley, that the only difference between a fossil and a recent animal is that one has been dead longer than the other, represents the spirit in which the study is being carried forward. [Illustration: Fig. 100.--E.D. Cope, 1840-1897.] With the establishment of the doctrine of organic evolution palæontology entered upon its modern phase of growth; upon this basis there is being reared a worthy structure through the efforts of the recent votaries to the science. It is neither essential nor desirable that the present history of the subject should be followed here in detail. The collections of material upon which palæontologists are working have been enormously increased, and there is perhaps no place where activity has been greater than in the United States. The rocks of the Western States and Territories embrace a very rich collection of fossil forms, and, through the generosity of several wealthy men, exploring parties have been provided for and immense collections have been brought back to be preserved in the museums, especially of New Haven, Conn., and in the American Museum of Natural History in New York City. Leidy, Cope, and Marsh.--Among the early explorers of the fossils of the West must be named Joseph Leidy, E.D. Cope (Fig. 100), and O.C. Marsh. These gentlemen all had access to rich material, and all of them made notable contributions to the science of palæontology. The work of Cope (1840-1897) is very noteworthy. He was a comparative anatomist equal to Cuvier in the extent of his knowledge, and of larger philosophical views. His extended publications under the direction of the United States Government have very greatly extended the knowledge of fossil vertebrate life in America. O.C. Marsh (Fig. 101) is noteworthy for similar explorations; his discovery of toothed birds in the Western rocks and his collection of fossil horses, until recently the most complete one in existence, are all very well known. Throughout his long life he contributed from his own private fortune, and intellectually through his indefatigable labors, to the progress of palæontology.