THE SHINGLE FORMATION. 223 



cient evidence of the former presence of glaciers over the region where 

 such moraines occur, while the presence of massive crystalline rocks, like 

 that shown in Fig. 35, often weighing several tons, at intervals over 

 the plains, and sometimes as far removed from the mountains as is the 

 present coast line, can best be accounted for on the supposition of float- 

 ing ice. 



The upheaval which has accomplished the final recovery of the Pata- 

 gonian plains from the sea began, as has been shown, with the close of 

 the Pliocene. It has continued uninterruptedly from that time and is still 

 going on, as will be shown by a careful examination of the deposits about 

 the mouths of almost any of the watercourses now entering the sea. In 

 many such places I have observed accumulations of recent shells, and 

 portions of the skeletons of whales and other cetaceans far inland, and at 

 altitudes to which the highest tides of this coast now never attain. Near 

 the mouth of the Rio Chico of the Gallegos, but some three miles inland, 

 there may be seen, almost buried in the shingle of the plain, a nearly 

 complete skeleton of a large whale, left stranded at that particular spot 

 when the sea still had access to that region. 



The deposition of the Shingle formation of Patagonia has, I believe, 

 been coincident with the recovery of this region from the sea, and, like the 

 movement which has accomplished the latter, it commenced with the close 

 of the Pliocene, has continued ever since, and is still going on. If I am 

 right in this supposition, we have only to study those phenomena which 

 are now presented at any one of the several places along this coast, where 

 land is being recovered from the sea, to arrive at a satisfactory explana- 

 tion of the deposition and present distribution of the shingle. 



The glaciers and, since their recession from the plains into the Andes, 

 the terminal moraines which they left during that recession, have been the 

 chief sources of the materials from which the deposits of shingle have been 

 derived. So long as the elevation of the region lying east of the Andes 

 had not proceeded so far as entirely to shut out the sea, many of the gla- 

 ciers, instead of terminating on the plains, would reach out into the numer- 

 ous deep bays and inlets of the latter and give rise to the formation of 

 great numbers of icebergs. These would be driven out to sea and, as they 

 melted, drop such stones and bowlders as they carried over the surfaces 

 of the still submerged lower plains lying to the eastward. As the eleva- 

 tion proceeded, and each of these plains was brought successively above 



