230 ANNUAL EEPOET SMITHSONIAN INSTITUTION^ 1915. 



as every one knows, is only one of the branches of the great Tertiary 

 chain ; it is the prolongation in the north of Africa of the mountain- 

 ous system of the Apennines. As to the true Alps, which are the 

 principal branch of the same chain, they may be foUow^ed without 

 difficulty as far as the Sierra Nevada, and even to Gibraltar. Under 

 the Strait of Gibraltar they are reunited to the Eif Mountains. 

 But the Rif , in which some geologists would see the continuation of 

 the entire Alpine system, certainly correspond to only a part of 

 this system; all of one northern band of Alpine folds, emerging 

 from under the nappes of the Sierra Nevada, moves toward the 

 west instead of turning toward Gibraltar. I see them, under the 

 recent terranes, crossing Andalusia, forming a narrow band on the 

 coast of Algarve, and finally, at Cape St. Vincent, abruptly cut 

 off and not showing any tendency toward " drowning," hiding them- 

 selves in the sea. Their direction, if prolonged, would lead us to 

 Santa Maria, the most southern of the Azores, where we observe 

 undisturbed Miocene sediments. 



Summing up, there are strong reasons for believing in the Atlantic 

 prolongation of the Tertiary folds, those of the Atlas Mountains 

 toward the Canaries, those of the Alps toward the southern islands 

 of the Azores, but nothing yet permits of either extending very far 

 or limiting very narrowly this prolongation. The sediments of 

 Santa Maria prove only this, that at the Miocene epoch — that is, 

 when the great Alpine movements were terminated in Europe — a 

 Mediterranean shore extended not far from this region of the Azores, 

 the shore of a continent or of a large island. Another shore of the 

 same Miocene sea passed near the Canaries. 



In every way the geography has singularly changed in the Atlantic 

 region in the course of the later periods of the earth's history; and 

 the extreme mobility of the bottom of the ocean, shown at the 

 present time by such a multiplicity of volcanoes and such an extent 

 of lava fields, surely dates from far back. Depressions during the 

 secondary period, enlarging the Mediterranean and causing the ruins 

 of the Hercynian chain to disappear; foldings in the entire Mediter- 

 ranean zone during the first half of the Tertiary era, modifying the 

 beds of this sea and causing mountainous islands to arise here or 

 there near its northern coast; collapses again at the close of the 

 Miocene, in the folded Mediterranean zone and in the two conti- 

 nental areas, continuing up to the final annihilation of the two con- 

 tinents and the obliteration of their shores; then, in the bottom of the 

 immense maritime domain resulting from these subsidences, the ap- 

 pearance of a new design whose general direction is north and south 

 and which conceals or, at the very least, partially obliterates the 

 former marking; the pouring out of the lavas, everywhere a little, 

 in the residual islands and even on the bottom of the seas, this pour- 



