46 REPORT — 1864. 



lead, and the speculations wliicli they suggest, require only to be named. How 

 to explain the all but universal glaciation of the mountain regions of Europe— 

 once, or perhaps twice, since the era of the Crag ; how to trace the course and 

 limits of those gelid waters which since that era rose to half the heiglit of 

 HelvelljTi and Snowdon ; how to account for the changes of physical geogi-aphy 

 which Allowed Hippopotami to be buried in the sediments of a Yorkshire river, 

 troops of Mammoths to crowd the Cotswold Hills, and the mingled remains of 

 Reindeer and jSIan to fill the caverns of the South of France— these and many 

 more questions of equal importance occupy the attention of geologists, and give a 

 special interest to the later geological periods. 



In each of these cases, and in all which come before geologists for interpretation, 

 there is one general rule : — we compare always the ancient phenomena with the 

 most similar effects we can find of forces now in action. 



As in existing natm-e the amount of eftect produced by known causes varies 

 with the conditions of each case — as the sun's eftect varies from hour to hour, from 

 day to night, from summer to winter, and from year to year — as the force of 

 movino- water is greater or less according to the slope of the ground, and the 

 sea's movement is modified by the age of the moon and the position of land — 

 so in earlier nature the combinations of phejiomena varied, and the measures of 

 efl'ect were modified accordingly. In another point of view the aspect of nature is 

 found to be variable, and subject to cycles of change, periods of gi-eater and less 

 efiect of particular forces which in their own nature are constant. The distance of 

 the earth from the sun is not constant, the form of its orbit is not constant, it was 

 not alwavs nor will always be nearer to the sun in winter than in sunmier. From 

 these varied conditions, which are measured by long astronomical periods, cycles of 

 oreater and less heating eftect on the earth in general, and on parts of it in parti- 

 cular, arise ; so that specitlations as to the causes of the differences of climate during 

 o-eolo<rical periods are entirely incomplete if we leave out of -view these real and 

 definite sources of terrestrial vicissitude. "Whether they are sufiicient, and justly 

 applicable to the facts established in geology', is a proper subject of deliberate 

 inquiry. 



Among the facts put in evidence by geology regarding the fonner condition of 

 the land and sea, none are so con\-incing of great change and systematic diversity as 

 the remains of plants and animals. By appeals to these innumerable -wntnesses, 

 conclusions of much importance are maintained, touching the greater warmth of the 

 carboniferous land, and the colder climate of the later csenozoic seas. By the same 

 testimonv, it appears that over every part of the eai-th's surface, in everj' class of 

 oro-anic life, the whole series of created forms has been changed many times. 



Have we measured these changes of climate, and assigned their true physical 

 causes ? Have we determined the law of the successive variations of life, and de- 

 clared the physiological principles on which tlie differences depend ? No ! the 

 variations of climate must be further investigated, the limits of specific diversity 

 more surely defined, before we can give clear answers to these critical questions. 



Late researches, partly arcbreological and partly geological, both in England and 

 France, have been held to prove the contemporaneity of Man and the Mammoth in 

 the northern zones of the world. Have we, then, been too confident in our belief that 

 the human period was long posterior to, and strongly marked off" from, that of the 

 Cavern Bear and the woolly Rhinoceros ? Did the races of Hysena and Hippopo- 

 tamus remain inhabitants of Europe till a comparatively modern epoch, or was Man 

 in possession of the earth in times far eai'lier than history and tradition allow ? 



The prevalent opinion seems to be, that as variations of tlie fonns of life are ex- 

 tremely slow in existing nature, for every case of considerable change in the pre- 

 dominant types of ancient plants and animals, very long intervals of time must be 

 allowed to' have elapsed. If in some thousands of years of human experience no 

 very material change has happened in our -w-ild plants or wild animals, or in cultivated 

 grains, or domestic bu-ds and quadrupeds, it is evident that no considerable change.? 

 of this kind can arise from such causes as are now in action vdthout the aid of 

 periods of time not contemplated in our chronology. I]8timated in this way, the 

 antiquity of the earth grows to be inconceivable — not to be counted by centimes, or 

 mvriads of years — not to be really compassed by the imderstanding of men, whose 



