casual visitants to a country should be ignored, but I do think that it is a wrong to science to enumerate, for examples, an European vagrant to America, never found but once, and not likely to recur again for an indefinite time, if ever, or an American bird that has been once found in Britain, in a line with the well-known members of the respective faunas. Their place would be most natural in an appendix or foot note, and they should at least be without the serial numeration, if such is given, of the catalogue of permanent and seasonal members of the fauna. Let me also protest, as I have done several times before, against the incorporation of Bassalian types with the species of littoral faunas nearest to them geographically. With catalogues and data, such as I have indicated, at hand, we could soon determine, as closely as practicable, the limits of most of our faunas, and the general attention now paid to natural history holds out the hope that the coming time may not long be deferred. In conclusion, I submit a few deductions that naturally result from our observations.

A distinction is to be made between the territory occupied by an association of animals and the occupants thereof, and the limits of faunas cannot be exactly correlated with territory, except in rare

cases.

The significance of animal types as indicators of zoogeographical regions is, other things being equal, in ratio to their recent development.

The fresh-water types are the best indicators of the early relations of the respective regions.

The flying, and especially migratory, types are the most accordant with the actual relations of land areas.

Temperature is a prime factor, and land a secondary, in the distribution of marine animals..

The lay of the land is a primary, and temperature a secondary, factor in the distribution of inland animals.

CERTAIN PHASES IN THE GEOLOGICAL HISTORY OF THE NORTH AMERICAN CONTINENT, BIOLOGICALLY CONSIDERED.*

By CHARLES A. WHITE.

It is quite certain that there has never been a time in the history of mankind when the thoughts of men were so eagerly turned to biological subjects as they are to-day; nor has there ever before been a time when an intelligent knowledge of them was so broadly diffused among cultivated persons. An earnest desire is everywhere manifested by such persons to obtain substantial knowledge concerning the animal and vegetable life of the earth, and of the broad significance of that life, which is revealed by a comparative study of its myriad forms. The investigator immediately finds that this subject, although it is so comprehensive and so complex, is only a fragment of a great history of life, which extends back through unnumbered ages. He finds himself at once confronted by questions concerning successive multitudes of former denizens of the earth, the physical conditions which prevailed when they existed, the probable lines of descent by which they came into being, and by which their successors have come down to the present time; and the manner in which those lines have probably originated and been preserved from destruction through successive geological periods.

This prevalent spirit of inquiry among men has been the cause of a vast amount of patient and exhaustive research, and it has also resulted in a large accumulation of knowledge. But it cannot be denied that every investigating naturalist, although he may fully accept the doctrine of evolution, finds the subject of the origin and derivation of the various groups of animals that now inhabit the earth, and those which have inhabited it during past geological time, to be beset with many difficulties and uncertainties.

* Presidential Address delivered at the Fourth Anniversary Meeting of the Society, January 25, 1884, in the Lecture Room of the U. S. National Museum.

As a rule, too, he finds that the questions which arise in connection with the probable manner in which the various groups of animals have originated and become distributed over the earth are too complex to allow of their reduction to even approximately simple propositions. Still, the accumulated results of the various and extensive investigations which naturalists have made of late years have placed the general subject of the evolution of organic forms in such a condition as a working hypothesis, that some of its various divisions may be treated with considerable detail, even with reference to extinct faunas. Furthermore, in a great number of cases, the facts which have been observed are of such a character as to warrant opinions of so important a nature that they may be legitimately used as a basis for philosophical discussions. It is mainly upon such facts and opinions as these that the following remarks are based; and while the conclusions and opinions which are here expressed are believed to be fully warranted by known facts, it is only too evident that much, which it is very desirable to know in this connection, still remains beyond our reach.

That I may more clearly present my subject, I submit the following statement of certain views which I hold in relation to it; and, for the purpose of greater conciseness of statement in the remarks which are to follow, I shall refer to those views somewhat as if they were supported by established and acknowledged facts.

The general subject of the probable origin of the different forms of animal life, and their perpetuation through geological time being so broad, I must confine myself to such small portions of it as my studies have led me to understand as having an important bearing upon the geological history of the North American continent. I must, furthermore, confine myself to such portions of the subject as relate to terrestrial life only, leaving largely out of consideration the subject of marine life.

Since the points I wish to present are somewhat disconnected by our present imperfect knowledge, I must trust to making their relevancy more apparent when I come to make the proposed application

of them. A discussion of formerly existing vegetable forms would also be of great interest, but I must omit all except incidental reference to that subject also.

In all investigations into the history of ancient life upon the earth, regard must be had to the functions that animals perform, and to the conditions under which those functions are executed. The requisite conditions for the performance of the physiological functions in the simplest animal forms, the Protozoa, for example, render it practically certain that the primary origin of animal life occurred in water; and it doubtless occurred in the sea. The first animal life having necessarily been of aqueous origin, we must assume that the first air-breathing animals were developed from those of aqueous respiration.

Fresh-water mollusks and fishes, especially the former, have, I believe, primarily become such by a change from their originally marine habitat, mainly by compulsion; that is, their progenitors lived in the sea and became land-locked by the unequal elevation of the sea bottom upon, or over which, they lived while the continental areas were in process of elevation. The waters of the districts thus inclosed and elevated above the level of the surrounding sea became first brackish, and then fresh, in consequence of the influx of fresh water from the drainage of the surrounding land, and a consequent outflow into the open sea. Those of the sea-born animals which became thus inclosed, and which were capable of conforming to the new conditions, did so, and peopled the river systems which were produced in connection with, and which succeeded, these fresh-water lakes. Those which could not thus conform to the new conditions became extinct; and as these appear to have constituted the larger part of every fauna which became landlocked in the manner referred to, we may reasonably conclude that the lines of descent of many of the groups of marine animals have been broken by this means.

River systems have resulted upon the disappearance, by final drainage, of the fresh-water lakes just mentioned, the inlets having