Professor Hartt, who accompanied Professor Agassiz in his South American travels, and published a valuable work called "The Geology of Brazil," describes drift-deposits as covering the province of Pará, Brazil, upon the equator itself. The whole valley of the Amazon is covered with stratified and unstratified and unfossiliferous {p. 38} Drift,[1] and also with a peculiar drift-clay (_argile plastique bigarrée_), plastic and streaked. Professor Hartt gives a cut from which I copy the following representation of drift-clay and pebbles overlying a gneiss hillock of the Serra do Mar, Brazil: ### DRIFT-DEPOSITS IN THE TROPICS. _a_, drift-clay; _f f_, angular fragments of quartz; _c_. sheet of pebbles; _d d_, gneiss in situ; _g g_, quartz and granite veins traversing the gneiss. But here is the dilemma to which the glacialists are reduced: If an ice-sheet a mile in thickness, or even one hundred feet in thickness, was necessary to produce the Drift, and if it covered the equatorial regions of Brazil, then there is no reason why the same climatic conditions should not have produced the same results in Africa and Asia; and the result would be that the entire globe, from pole to pole, must have rolled for days, years, or centuries, wrapped in a continuous easing, mantle, or shroud of ice, under which all vegetable and animal life must have utterly perished. [1. "Geology of Brazil," p. 488.] {p. 39} And we are not without evidences that the drift-deposits are found in Africa. We know that they extend in Europe to the Mediterranean. The "Journal of the Geographical Society" (British) has a paper by George Man, F. G. S., on the geology of Morocco, in which he says: "Glacial moraines may be seen on this range nearly eight thousand feet above the sea, forming gigantic ridges and mounds of porphyritic blocks, in some places damming up the ravines, and at the foot of Atlas are enormous mounds of bowlders." These mounds oftentimes rise two thousand feet above the level of the plain, and, according to Mr. Man, were produced by glaciers. We shall see, hereafter, that the sands bordering Egypt belong to the Drift age. The diamond-bearing gravels of South Africa extend to within twenty-two degrees of the equator. It is even a question whether that great desolate land, the Desert of Sahara, covering a third of the Continent of Africa, is not the direct result of this signal catastrophe. Henry W. Haynes tells us that drift-deposits are found in the Desert of Sahara, and that-- "In the _bottoms_ of the dry ravines, or wadys, which pierce the hills that bound the valley of the Nile, I have found numerous specimens of flint axes of the type of St. Acheul, which have been adjudged to be true palæolithic implements by some of the most eminent cultivators of prehistoric science."[1] The sand and gravel of Sahara are underlaid by a deposit of clay.