Louis Agassiz: His Life and Correspondence

by Louis Agassiz

With reference to the glacial period he anticipated still more positive results. In the same letter the following passage occurs: "There is, however, still one kind of evidence wanting, to remove all doubt that the greater extension of glaciers in former ages was connected with cosmic changes in the physical condition of our globe. Namely, all the phenomena relating to the glacial period must be found in the southern hemisphere, accompanied by the same characteristic features as in the north, but with this essential difference,—that everything must be reversed. The trend of the glacial abrasions must be from the south northward, the lee-side of abraded rocks must be on the north side of the hills and mountain ranges, and the boulders must have traveled from the south to their present position. Whether this be so or not, has not yet been ascertained by direct observation. I expect to find it so throughout the temperate and cold zones of the southern hemisphere, with the exception of the present glaciers of Terra del Fuego and Patagonia, which may have transported boulders in every direction. Even in Europe, geologists have not yet sufficiently discriminated between local glaciers and the phenomena connected with their different degrees of successive retreat on the one hand; and, on the other, the facts indicating the action of an extensive sheet of ice moving over the whole continent from north to south. Among the facts already known from the southern hemisphere are the so-called rivers of stone in the Falkland Islands, which attracted the attention of Darwin during his cruise with Captain Fitzroy, and which have remained an enigma to this day. I believe it will not be difficult to explain their origin in the light of the glacial theory, and I fancy they may turn out to be ground moraines similar to the 'horsebacks' in Maine.

"You may ask what this question of drift has to do with deep-sea dredging? The connection is closer than may at first appear. If drift is not of glacial origin, but is the product of marine currents, its formation at once becomes a matter for the Coast Survey to investigate. But I believe it will be found in the end, that so far from being accumulated by the sea, the drift of the Patagonian lowlands has been worn away by the sea to its present outline, like the northern shores of South America and Brazil.". . .

This is not the place for a detailed account of the voyage of the Hassler, but enough may be told to show something of Agassiz's own share in it. A journal of scientific and personal experience, kept by Mrs. Agassiz under his direction, was nearly ready for publication at the time of his death. The two next chapters, devoted to the cruise of the Hassler, are taken from that manuscript. A portion of it appeared many years ago in the pages of the "Atlantic Monthly."

CHAPTER 23.

1871-1872: AGE 64-65.

Sailing of the Hassler.
Sargassum Fields.
Dredging at Barbados.
From the West Indies to Rio de Janeiro.
Monte Video.
Quarantine.
Glacial Traces in the Bay of Monte Video.
The Gulf of Mathias.
Dredging off Gulf of St. George.
Dredging off Cape Virgens.
Possession Bay.
Salt Pool.
Moraine.
Sandy Point.
Cruise through the Straits.
Scenery.
Wind Storm.
Borja Bay.
Glacier Bay.
Visit to the Glacier.
Chorocua Bay.

The vessel was to have started in August, but, owing to various delays in her completion, she was not ready for sea until the late autumn. She finally sailed on December 4, 1871, on a gray afternoon, which ushered in the first snow-storm of the New England winter. Bound for warmer skies, she was, however, soon in the waters of the Gulf Stream, where the work of collecting began in the fields of Sargassum, those drifting, wide-spread expanses of loose sea-weed carrying a countless population, lilliputian in size, to be sure, but very various in character. Agassiz was no less interested than other naturalists have been in the old question so long asked and still unanswered, about the Sargassum. "Where is its home, and what its origin? Does it float, a rootless wanderer on the deep, or has it broken away from some submarine attachment?" He had passed through the same region before, in going to Brazil, but then he was on a large ocean steamer, while from the little Hassler, of 360 tons, one could almost fish by hand from the Sargassum fields. Some of the chief results are given in the following letter.

TO PROFESSOR PEIRCE.

ST. THOMAS, December 15, 1871.

. . .As soon as we reached the Gulf Stream we began work. Indeed, Pourtales had organized a party to study the temperatures as soon as we passed Gay Head, and will himself report to you his results. My own attention was entirely turned to the Gulf weed and its inhabitants, of which we made extensive collections. Our observations on the floating weed itself favor the view of those who believe it to be torn from rocks, on which Sargassum naturally grows. I made a simple experiment which seems to me conclusive. Any branch of the sea-weed which is deprived of its FLOATS sinks at once to the bottom of the water, and these floats are not likely to be the first parts developed from the spores. Moreover, after examining large quantities of the weed, I have not seen a single branch, however small, which did not show marks of having been torn from a solid attachment.