348 J. B. Hatcher — Geology of Southern Patagonia. 



I have already stated that the deposition and distribution of 

 the great bowlder formation was accomplished by the com- 

 bined action of water and ice. The facts which have led to 

 this conclusion are the great quantity of material left as rounded 

 hillocks, composed of heterogeneous masses of angular rocks, 

 often of great size, polished bowlders and much fine-grained, 

 silted material, occurring as moraines all along the base of the 

 mountains and sometimes extending for some distance out on 

 the plains. Another fact also observed and bearing directly 

 upon this question is the distribution throughout this forma- 

 tion of immense bowlders, which could not possibly have been 

 transported to their present position by any other agency than 

 that of ice. The number of these large, massive bowlders 

 rapidly decreases to the eastward after reaching a point about 

 thirty miles east of the Cordilleras, but they are found, though 

 rarely, even as far east as the present coast. As an instance 

 of this I may mention that one of these bowlders, weighing 

 several thousand pounds, may be seen on the bluffs of the south 

 side of the Rio Chico about ten miles below the mouth of Rio 

 Chalia. It lies on the north side of and only a few yards 

 from the road which leads from the port of Santa Cruz to the 

 settlements on the lower Rio Chico. Its position is approxi- 

 mately shown on the map at the point marked +B. From the 

 present position of this rock, weighing not less than 6000 

 pounds, to the mountains, is a distance of 200 miles, and it 

 does not seem possible that this immense bowlder could have 

 been transported that distance by any other agency than that 

 of ice. I therefore conclude that, along with the elevation 

 there were in the Cordilleras great accumulations of snow and 

 ice, which produced glaciers extending out beyond the foot 

 hills of the mountains even as far as the, at that time, eastern 

 border of the sea. The glaciers no doubt transported most of 

 the material now constituting the great bowlder formation 

 from the Cordilleras to the sea, where it was afterwards dis- 

 tributed over the region to the eastward by the combined 

 action of water and ice, either in the form of icebergs or float- 

 ing shore and river ice. This would account for the enor- 

 mously greater development of the bowlder formation near 

 the Cordilleras than distant from them ; for the gradually de- 

 creasing size of the rocks of which it is formed as we proceed 

 eastward from the mountains, both of which facts have been 

 observed and commented upon by Darwin ; and also for the 

 occasional occurrence in the formation of large bowlders in 

 places far removed from the mountains, and which were doubt- 

 less carried by icebergs direct from the glaciers to their present 

 positions. 





