Fknton — Recent Pampa and other Formations in Patagonia. 601 



or less abrupt; and the laud rises to the level of the pampas, often in a series 

 of well-marked terraces. From the top of the last terrace on one side to the 

 corresponding one ou the opposite side is in some places as much as fifteen to 

 twenty miles in extent ; in others it is not more than one to two miles. 



In Plate XLVII, fig. 1, whicli represents the middle reaches of the 

 Gallegos E.iver, it will be noticed that the action which operated in cutting 

 out these river-valleys and canadones was not only capable of wearing down 

 the ordinary pampa formation, which consists to a large extent of shingle and 

 clay, but was capable also of cutting its way through considerable thicknesses 

 of hard basalt. In this photograph the telegraph posts are seen standing in the 

 bed of the river- valley, which in the place shown is upwards of two miles wide. 

 A is the opposite bank lower down where the river-valley curves round to 

 the right : it is a table of basalt lying on pampa formation, and is about 

 400 feet above the river. B is part of a volcanic cone, the side of which has 

 been cut away and swept clean, leaving practically no fragments; it is 

 better seen in fig. 2. It abuts directly on to tlie river-valley, where its 

 continuity ends abruptly, and it shows all the evidences of comparatively 

 recent activity, so far as the serrated summit is concerned ; yet the sides and 

 base show that some considerable action took place at no very distant date 

 which caused them to be swept so clean. It is impossible to conceive that 

 when tlie river was already in its present position, a great outburst of volcanic 

 activity could have occurred without pouring a huge sheet of lava down the 

 river- valley. No such lava-sheet, however, exists ; while, on the other hand, 

 the rich soil of the valley extends right to the base of this cone ; it is to be 

 presumed, therefore, that the valley has been cut down since the outpouring 

 of the lava. In point C the phenomena are more striking than in point B, 

 for liere we have a gigantic table of supra-pampean basalt upwards of 

 1000 feet high, rising abruptly and steeply from tlie level valley below, and 

 terminating at the top in a sheer precipice of about 300 feet of solid volcanic 

 rock. Under point D in fig. 1 is a deep canadon or gorge, dowu which a 

 small river known as the Gallegos Chico runs. This caiiadon is a narrow 

 deep cutting, the sides of which are more or less pi-ecipitous : it runs between 

 tables C and E, which are overlain by supra-pampean basalt. From its 

 appearance the basalt would seem to have been continuous at one time over 

 D. Tables and E extend up to over 1000 feet at the back, so that the 

 action which cut down the Gallegos Chico gorge through hundreds of feet of 

 solid basalt, almost as hard as iron, must have been a very considerable one, 

 especially when we note that this all probably took place since Middle 

 Quaternary times. 



Not only here, but right througli this part of Patagonia, are to be found 



4u2 



