Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/932

 with mud from the grinding of the glacier on the infrajacent rocks — in fact, from the washings of the moraine profonde. This stream flows in a torrent the whole year round, and in every case which I know of (in the Arctic Regions) reaches the sea eventually, though, no doubt, parting on the way with some small amount of its suspended mud. After it reaches the sea it discolours the water for miles, finally depositing on the bottom a thick coating of impalpable powder. When this falls in the open sea it may be scattered over a considerable space ; but when (as in most cases) it falls in narrow long fjords, it collects at the bottom, shoaling up these inlets for several miles from their heads, until, in the course of time, the fjord gets wholly choked up, and the glacier seeks another outlet or gets choked up with bergs, which slowly plough their way through, the deep banks of clay, until they get so consolidated together as to shut off the land altogether 1. Supposing that the deposit only reaches 3 inches in the year, there is a bank or flat 25 feet thick formed in the course of a century. However, any one who has seen these muddy sub-glacier streams, and the way in which they deposit their mud, must be convinced that this estimate is far below the mark, and that an important geological deposit, which has never been rightly accounted for (if even noticed, as far as my observation goes), is forming off the coast of Greenland and wherever its great glaciers protrude into the deep quiet fjords. It ought also to be noticed that the fjords which have been the scenes of old ice- streams, in almost every instance end in a valley at the head, this valley being due, first, to the glacier which reclined on it and hollowed it out, and, secondly and further down, to the filling up of it by the glacier-clay. This form of fjord is not only common in Greenland, but also in every other part of the world where I have studied their form and formation.

After carefully examining and studying this clay, I can find no appreciable difference between it and the brick-clay, or fossiliferous Boulder-clay. Mr. Milne Home 2, among other arguments against the theory that Boulder-clay has been formed by land-ice, remarks that he saw nothing forming in Switzerland at all comparable to Boulder-clay. Reserving to ourselves a doubt on that subject, I can only say that long after my opinion regarding the identical character of the subglacial-stream clay and the fossiliferous brick-clay was formed, a very illustrious Scandinavian Arctic explorer visited Edinburgh, and declared, as soon as he saw the sections of Boulder- clay exhibited near that city, that this was the very substance he saw forming in the Spitzbergen ice-fjords. Many theoretical writers, however, confound the ordinary non- stratified azoic clay, and the finer, stratified fossiliferous clay.

In this clayey bed the Arctic Mollusca and other marine animals find a congenial home, and burrow into it in great numbers. How-

1 I am glad to find that, independently, this identical view is held by Mr. J. W. Tayler, who resided for several years in Greenland, Proc. Roy. Geogr. Soc. vol. v. p. 90 (1861).

2 Trans. Roy. Soc. Edin. vol. xxv. p. 661.