Louis Agassiz: His Life and Correspondence

by Louis Agassiz

DEAR SIR,

Far from considering your request a tax upon my time, it gives me the greatest pleasure to have an opportunity of laying before you some statements and reflections, which I trust may satisfy you that geology and natural history can be made subservient to the great interests of a civilized community, to a far greater extent than is generally admitted.

The question of the harbor of Boston, for instance, has a geological and zoological side, thus far only indirectly considered. In order to ascertain whence the materials are derived which accumulate in the harbor, the shores ought to be studied geologically with a kind of accuracy and minuteness, never required by geological surveys made for economical purposes. The banks of the harbor, wherever it is not rock-bound, consist of drift, which itself rests upon the various rock formations of the district. Now this drift, as I have ascertained, formerly extended many miles beyond our present shores, and is still slowly washed away by the action of tides, winds, and currents. Until you know with precision the mineralogical composition of the drift of the immediate vicinity, so accurately indeed as to be able to recognize it in any new combination into which it may be brought when carried off by the sea, all your examination of soundings may be of little use. Should it, however, be ascertained that the larger amount of loose material spreading over the harbor is derived from some one or other of the drift islands in the bay, the building of sea-walls to stop the denudation may be of greater and more immediate use than any other operation. Again, it is geologically certain that all the drift islands of the harbor have been formed by the encroachment of the sea upon a sheet of drift, which once extended in unbroken continuity from Cape Ann to Cape Cod and farther south. This sheet of drift is constantly diminishing, and in centuries to come, which, notwithstanding the immeasurable duration of geological periods, may be reached, I trust, while the United States still remains a flourishing empire, it will be removed still further; so far indeed, that I foresee the time when the whole peninsula of Cape Cod shall disappear. Under these circumstances, it is the duty of a wise administration to establish with precision the rate and the extent of this destruction, that the coming generations may be forewarned. In connection with this I would advise the making of a thorough survey of the harbor, to ascertain the extent of rock surface and of drift, and the relative position of the two, with maps to show their relations to the different levels of the sea, whereby the unequal action of the tides upon the various beaches may be estimated.

The zoological side of the question relates to the amount of loose materials accumulating in consequence of the increase of animal and vegetable life, especially of those microscopic beings which, notwithstanding their extraordinary minuteness, form in course of time vast deposits of solid materials. Ehrenberg has shown that the harbor of Wismar, on the Prussian coast of the Baltic, is filling, not in consequence of the accumulation of inorganic sediments, but by the rapid increase and decay of innumerable animalcules. To what extent such deposits may accumulate has also been shown by Ehrenberg, who ascertained, many years ago, that the city of Berlin rests upon a deposit of about eighteen feet in thickness, consisting almost exclusively of the solid parts of such microscopic beings. These two cases may suffice to show how important may be a zoological investigation of the harbor deposits.

I need hardly add that the deposits floated into the harbor, by the numerous rivers and creeks which empty into it, ought to be investigated with the same care and minuteness as the drift materials. This investigation should also include the drainage of the city.

But this is only a small part of the application I would recommend to be made of geological and zoological knowledge, to the purposes of the Coast Survey. The reefs of Florida are of the deepest interest, and the mere geodetic and hydrographic surveys of their whole range would be far from exhausting the subject. It is my deliberate opinion that the great reefs of Florida should be explored with as much minuteness and fullness as the Gulf Stream, and that the investigation will require as much labor as has thus far been bestowed on the Gulf Stream. Here again geological and zoological knowledge is indispensable to the completion of the work. The reef is formed mainly by the accumulation of solid materials from a variety of animals and a few plants. The relations of these animals and plants to one another while alive, in and upon the reef, ought to be studied more fully than has been the case heretofore, in order to determine with certainty the share they have in the formation of these immense submarine walls so dangerous to navigation. The surveys, as they have been made thus far, furnish only the necessary information concerning the present form and extent of the reef. But we know that it is constantly changing, increasing, enlarging, spreading, rising in such a way and at such a rate, that the surveys of one century become insufficient for the next. A knowledge of these changes can only be obtained by a naturalist, familiar with the structure and mode of growth of the animals. The survey I made about fifteen years ago, at the request of your lamented predecessor, could only be considered as a reconnaissance, in view of the extent and importance of the work. I would, therefore, recommend you to organize a party specially detailed to carry on these investigations in connection with, and by the side of, the regular geodetic and hydrographic survey. Here, also, would geological knowledge be of great advantage to the explorer. In confirmation of my recommendation I need only remind you of a striking fact in the history of our science. More than thirty years ago, before Dana and Darwin had published their beautiful investigations upon the coral reefs, a pupil of mine, the late Armand Gressly, had traced the structure and mode of growth of coral reefs and atolls in the Jura mountains, thus anticipating, by a geological investigation, results afterward obtained by dredging in the ocean. The structure of the reefs of our shores is, therefore, more likely to be fully understood by one who is entirely familiar with zoology and geology than by a surveyor who has no familiarity with either of these sciences.

There is another reason why I would urge upon you the application of natural sciences to the work of the survey. The depth of the ocean is a great obstacle to a satisfactory exploration of its bottom. But we know now that nearly all dry land has been sea bottom before it was raised above the level of the water. This is at least the case with all the stratified rocks and aqueous deposits forming part of the earth's crust. Now it would greatly facilitate the study of the bottom of the sea if, after ascertaining by soundings the general character of the bottom in any particular region, corresponding bottoms on dry land were examined, so that by a comparison of the one with the other, both might be better understood. The shoals of the southern coast of Massachusetts have been surveyed, and their position is now known with great accuracy; but their internal structure, their mode of formation, is only imperfectly ascertained, owing to the difficulty of cutting into them and examining in situ the materials of which they are composed. Nothing, on the contrary, is easier than to explore the structure or composition of drift hills which are cut through by all our railroad tracks. Now the shoals and rips of Nantucket have their counterparts on the main-land; and even along the shores of Boston Harbor, in the direction of Dorchester and Milton, such shoals may be examined, far away from the waters to which they owe their deposits. Here, then, is the place to complete the exploration, for which soundings and dredgings give only imperfect information.

I need not extend these remarks further in order to satisfy you of the importance of geological and zoological researches in connection with the regular operations of the Coast Survey. Permit me, however, to add a few words upon some points which, as it seems to me, belong legitimately to the Coast Survey, and to which sufficient attention has not yet been paid. I allude, first, to the salt marshes of our shores, their formation and uses, as well as their gradual disappearance under the advance of the sea; second, to the extended low islands in the form of reefs along the coast of the Southern States, the bases of which may be old coral reefs; third, the form of all our estuaries, which has resulted from the conflict of the sea with the drift formation, and is therefore, in a measure, a geological problem; fourth, the extensive deposits of foraminifera along the coast, which ought to be compared with the deposits of tripoli found in many tertiary formations; fifth, the general form and outline of our continent, with all its indentations, which are due to their geological structure. Indeed, the shore everywhere is the result of the conflict of the ocean with the rock formation of the land, and therefore as much a question for geology as geodesy to answer.

Should the preceding remarks induce you to carry my suggestions into practical operation, be assured that it will at all times give me the greatest pleasure to contribute to the success of your administration, not only by advice, but by actual participation in your work whenever that is wanted. The scientific men of America look to you for the publication of the great results already secured by the Coast Survey, well knowing that this national enterprise can only be benefited by the high-minded course which has at all times marked your intellectual career.

Ever truly your friend,