928 REPORT— 1898. 



north-west, a total length of ahout 100 miles, nearly to Puan. In 1859 I spent a 

 turbulent period of several months among these mountains, as a member of a 

 commissio'.i charged to explore the south-western frontier of Buenos Ayres, which 

 was then being raided by the Patagonian, Araucanian, and Pampa tribes of 

 savages. Referring to my old field-book, I find evidences that some of my notes 

 were made in a huriy. 



The greatest bulk of the Ventana range appears to be gathered near the highest 

 peak of the Curamalal section, the elevation of which, by trigonometric measure- 

 ment, I found to be 3,363 feet above sea-level, and the Ventana peak 3,563 feet. 

 The inclination of their strata is from 60° to 85°, dipping, with little variation, 

 to the north-east. On their south-west slopes, so far as we explored them, these 

 mountains are composed of extremely hard quartz rock, white, pink, and other 

 colours. In many places it was cut into large rhomboidal-shaped solids. 



The highly calcareous, argillaceous rock-cap of the plain which lies between 

 the Ventana and Bahia Blanca slopes west-south-west, its elevation at the 

 southern foot of the Ventana range being about 600 feet, and at Nueva Roma 

 about 230 feet, above sea-level. 



Scattered over the surface of this plateau are many hollows, which in some 

 instances are 100 feet below the general level. At their bottoms small lagoons 

 are frequently found. 



On the northern slope of the culminating peak of the Ventana I found a con- 

 glomerate of rounded quartz pebbles, cemented by sandy, ferruginous matter. I 

 have seen specimens of similar conglomerate from the north-west slope of the 

 Curamalal range. I do not know the elevation of the bed which I found, but, for 

 several reasons, believe it to be about 1,200 feet above sea-level. It was, m 

 great part, cemented to the quartz rock of the mountain, although masses of it, 

 cubic yards in volume, had broken down or become displaced. Darwin states that 

 from 300 to 400 feet above the plain on the south side of the Ventana (' estimated 

 at 840 feet elevation by some Spanish officers ') he ' found a few small patches of 

 conglomerate and breccia, firmly cemented by ferruginous matter to the abrupt and 

 battered face of the quartz, traces being thus exhibited of ancient sea action.' He 

 thus estimates the height of that which he found on the south side of the 

 mountain at, approximately, the same as that which I found on the north side. 



Explorers differ as to the character and structure of the great belt of dunes 

 which stretches along the coast fi'om Cape San Antonio to Bahia Blanca. I am 

 familiar with them for a distance of only seventy miles east of the latter place, 

 along which extension they are massed to their greatest breadth and height. Per- 

 haps an unpublished leaf from my note-book of 1859 will enable you to realise 

 what they are as I saw them : — ' We proceeded to explore the course of the river 

 Mostazas among the dunes. For seven miles we forced our horses over sand hills 

 and through marshes and lagoons, although they sank to their knees at every step, 

 and frequently floundered to their breasts in the burrows of the Tuco-tucc, the 

 Ctenomi/^ magellanica, about the size of a small rat. At last they lay down com- 

 pletely exhausted. Far to the east, we could still distinguish lagoons, but not a 

 break in the coast line gave indication of the outlet of the river, while, all around 

 us, the bare sand-hills reflected the sun with painful brilliancy. The exhausted 

 condition of our horses obliged us to return dismounted. The dunes near the coast 

 are composed of pure quartz sand of every colour, nearly all of it translucent. As 

 they extend towards the interior, they have a slight mixture of earth, until their 

 inland line is found to contain a preponderance of light, pulverised soil. Gradually 

 a scanty vegetation appears, until, bordering the fertile lands, they are covered 

 with coarse grass and a few stunted shrubs. Viewed from the north, they have an 

 abrupt descent towards the west. Their coast line is about 110 feet high on 

 an average, but inland they are of every elevation from 5 to 100 feet. The 

 south-west gales violently agitate them, "and cloud the air with their materials. 

 Frequently, bowl-shaped excavations are found near their summits, which appear 

 like works of art, so regularly are they scooped out by the wind, which must have 

 been of terrific force. One of these, a detached hill of sand and dust, on the Sauce 

 Grande River, about twelve miles from the coast, has had at least 5,000 cubic yards 



