view. The best means for learning their ratio I think to be found in the changes of faunas and floras since the beginning of the Tertiary era, using especially the marine molluscan faunas as most valuable for this comparison. Scarcely any species of marine mollusks have become extinct or undergone important changes during the Glacial and Recent periods, but since the Eocene dawn of the Tertiary nearly all of these species have come into existence. Judged upon this basis, the Tertiary era seems probably fifty or a hundred times longer than the Ice age and subsequent time; in other words, it may well have lasted two millions or even four millions of years. Taking the mean of these numbers, or three million years, for Cenozoic time, or the Quaternary and Tertiary ages together, we have precisely the value of Professor Dana's ratios which he himself assumes for conjectural illustration, namely, 48,000,000 years since the Cambrian period began. But the diversified types of animal life in the earliest Cambrian faunas surely imply a long antecedent time for their development, on the assumption that the Creator worked before then as during the subsequent ages in the evolution of all living creatures. According to these ratios, therefore, the time needed for the deposition of the earth's stratified rocks and the unfolding of its plant and animal life must be about a hundred millions of years. Reviewing the several results of our different geologic estimates and ratios supplied by Lyell, Dana, Wallace, and Davis, we are much impressed and convinced of their approximate truth by their somewhat good agreement among themselves, which seems as close as the nature of the problem would lead us to expect, and by their all coming within the limit of 100,000,000 years which Sir William Thomson estimated on physical grounds. This limit of probable geologic duration seems therefore fully worthy to take the place of the once almost unlimited assumptions of geologists and writers on the evolution of life, that the time at their dis posal has been practically infinite. No other more important conclusion in the natural sciences, directly and indirectly modifying our, conceptions in a thousand ways, has been reached during this century. The error by which Mr. McGee, in the estimate stated. in the early part of this article, wanders so far astray, consists in his relying largely on Dr. Croll's theory for the cause of the Glacial period, whereby he concludes that this period was of great length and that the ice-sheets were due to as tronomic conditions while the land throughout the Ice age had somewhat approximately its present height, with only moderate uplifts and depressions. Drawing his ratios of Postglacial and Glacial time, and of the preceding early Quaternary or late Tertiary epoch to which the Lafayette formation belongs, from the amounts of stream erosion, he has supposed the conditions then similar to those of the present time, so that the relative durations of these epochs may be estimated from their excavation of valleys by water But it seems preferable, as before noted, to refer the Ice age to great elevation of the land, whereby the erosion of streams would be caused to proceed very much more rapidly than if the country were as low as now. With an altitude of our Atlantic coastal plain and whole continental area westward 3,000 feet higher than now, the valley-cutting may have gone forward twenty or a hundred times faster than to-day, or even near to the coast a thousand times faster than now. The factor with which Mr. McGee starts on the multiplication of the earlier ratios to change them to years is evidently far too large, and it gives therefore for all the geologic eras and for the earth's total age too vast figures probably by twentyfold to a hundredfold. courses. Anthropologists, not less than geologists, have a lively interest in the estimates and measurements of the length of the Glacial and Recent periods, for the earliest reliable testimony of man's existence comes to us from the Ice age both in North America and Europe. Confining our attention to the observations which prove that men were living on our continent as contemporaries of its northern ice-sheet, we have many independent and widely separated localities where traces of man's presence during the Glacial period have been found. Under the beach ridge of gravel and sand on the south side of Lake Iroquois, the Glacial representative of Lake Ontario, charred sticks, with ashes and stones laid to form a rude hearth, were discovered about 18 feet below the surface in digging a well in Gaines township, Orleans county, N. Y. Lake Iroquois was dammed on the northeast by the receding continental ice-sheet and outflowed by way of the Mohawk and Hudson. The hearth and fire were made, according to Mr. G. K. Gilbert, "not long after the establishment of the Mohawk outlet and during its continuance." To a much earlier stage of the glacial retreat we must refer the extensive gravel deposits of the Delaware River in the vicinity of Trenton, N. J., in which Dr. C. C. Abbott, Prof. F. W. Putnam, and others have found many palæolithic implements and chipped fragments of argillite. Somewhat farther south, in Delaware, Mr. Hilborne T. Cresson has found similar palæoliths in glacial gravel belonging to a still earlier part of the Ice age, probably deposited during the maximum extension of the ice-sheet. Other localities where palæoliths have been discovered in glacial gravel and sand beds, formed during the departure of the ice, are Newcomerstown, on the Tuscarawas River, in eastern Ohio; on the Little Miami River at Loveland and Madisonville, in southwestern Ohio; on the East Fork of the White River at Medora, in southern Indiana; and on the upper Mississippi at Little Falls, in central Minnesota. Again, in one of the beach ridges of the Glacial Lake Agassiz, held in the basin of the Red River of the North and of Lake Winnipeg by the barrier of the waning ice-sheet, Mr. J. B. Tyrrell has found chipped fragments of quartzite, evidently of human work manship, contemporaneous with the rounded gravel and wave-worn sand of the beach. West of the Rocky Mountains, also, an obsidian spear-head was discovered by McGee in the sediment of the Quaternary Lake Lahontan; and stone mortars, pestles, and even human bones, including the famous Calaveras skull, have been obtained by Whitney, King, Becker, Wright and others, from the gold-bearing gravels under the lava of Table Mountain, California. Though these last are south of the continental drift sheet, they seem referable, on sufficient geologic evidences, to the Pleistocene or Glacial period. At one time the Californian discoveries were believed by some to prove man's presence there during the Pliocene or closing period of the Tertiary era, far longer ago than the Ice age; but no indisputable proof, nor even apparently reliable evidence, for so great antiquity of man has been brought to light in any part of the world. Homo sapiens, as Professor LeConte stated in discussions of this subject at the meeting of the American Association last August in Rochester, N. Y., must be regarded, in the present stage of our knowledge, as restricted to the Quaternary era, although his anthropoid ancestors may have begun as far back as in Pliocene or Miocene time their ascent toward man's present intellectual and spiritual eminence. ARTICLE VIII. THE HISTORICAL STUDY OF CHRISTIANITY. BY PROFESSOR ARTHUR CUSHMAN MCGIFFERT, LANE THEOLOGICAL SEMINARY. CONVENIENTLY, though somewhat broadly and ambiguously, my subject may be styled: "The Historical Method applied to the Study of Christianity," or more briefly, "The Historical Study of Christianity." The wide use of the historic method is one of the marked features of the intellectual life of the present age. In all branches of knowledge its influence has been felt, and a revolution, second only to that which connects itself with the name of Francis Bacon, has been accomplished by it in our scientific thinking. The historic method, in fact, controls all lines of study and investigation. Whether applied to the works of nature or to the works of man, it is the same: in the one case, it gives us the theory of evolution; in the other, human history, which in the modern view is simply the account of an evolution in the sphere of the humanities. Christian thinking, as is always the case, has felt the influence of the spirit of the age, and has become historical. Not that the study of Christian history is a new thing, but that the historical study of Christianity is; for the conception of history and the historic method have undergone a great change since Eusebius wrote his ἱστορία ἐκκλησιαστική in ten books. Το him the history of the church was a drama in which two great opposing forces-God and Satan-were struggling for the mastery. All heresies, schisms, and persecutions were the work of Satan, who by means of them attempted to corrupt and rend 1 Opening address delivered at Lane Theological Seminary, Sept. 15, 1892. |