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XXXVIII. 



NOTES ON RECENT PAMPA AND OTHER FORMATIONS IN 



PATAGONIA. 



By E. G. FENTON (Rio Gallegos, Argentina). 



[communicated by PROFESSOll GKENVII.I.E A. J. COLE, M.U.I. A., F.G.S.] 



(Plate XLVil.) 



[Read Februaky 25. Published May 15, 1913.] 



On the plains of southern Patagonia, between the chain o£ the " Cordillera " 

 (tail of the Andes) and the Atlantic Ocean, there are to be found many points 

 of great interest to the geologist, especially with regard to the late Tertiary 

 and Quaternary formations. 



The present paper is an amplification of various notes taken by the writer 

 during the many journeys which he has made through the district of 

 Rio Gallegos, Argentine Republic, in the course of five years of medical 

 practice. It is hoped that they may usefully supplement the work already 

 done on glacial phenomena in S. America,^ since the conclusions are the result 

 of independent observations in the field. 



To the westward, west by south, and west by north of the town of Gallegos, 

 there is a large district of over 100 miles in extent, in which the pampa is 

 more or less buried under vast sheets of basaltic lava, the latter rising here 

 and there extensively over the plains to form cones and craters. 



The basalt in many places exhibits such a rugged and serrated appearance, 

 and shows sucli little weathering, that one would, on superficial examination, 

 be inclined to think that it was not more than a century or two old ; yet, as 

 will be seen in the sequel, it must have been poured out at a very remote 

 period, so far as the history of the human race is concerned. 



The next feature of interest on going over the "pampas" is the number 

 of deep-river beds and canadoues which are met with. The river-beds vary 

 in breadth from half a mile to perliaps three miles, and have been cut down 

 below the level of the surrounding pampas to depths varying from a few 

 hundred to over a thousand feet. The sides of these river-valleys are more 



' See, for iastimce, G. Steiumimu, " Tiber Diluvium iu Siid-Amerika," Monatsber. deutsch. geol. 

 Gesell., 1906, Nr. 8/10, 



