172 PATAGONIAN EXPEDITIONS: NARRATIVE. 



This lake lies in a deep valley, at an elevation of scarcely more than 

 one hundred meters above the level of the sea. To the eastward this 

 valley extends for many miles, connecting with that of White Lake and 

 the basalt canons still farther to the east. The divides separating Lake 

 Pueyrredon from White Lake and Rio Blanco and the latter from the 

 basalt canons lying east of Lake Gio, are very low and consist chiefly, if 

 not wholly, of glacial materials. The valley proper is continuous and 

 forms one deep, broad and uninterrupted trench, extending eastward 

 from Lake Pueyrredon for a distance of some fifty miles, where it is 

 abruptly contracted and thence becomes a deep, narrow defile, continued 

 for an unknown distance, with rugged enclosing walls, composed of igne- 

 ous and sedimentary rocks of varying age and character. Immediately 

 south of the eastern extremity of Lake Pueyrredon a rather precipitous 

 bluff rises abruptly to an altitude of five thousand feet above the waters 

 of the lake, as shown in Fig. 21. The rocks composing this are of 

 Cretaceous and Tertiary age and of sedimentary origin, save some fifty 

 feet of basalt which separates the uppermost Cretaceous from the low^er- 

 most Tertiary material. The different strata composing the bluff are, for 

 the most part, well displayed in the face of the cliff, while, as I subse- 

 quently learned, there are extensive exposures of the uppermost beds in 

 a region of bad lands at the summit. 



I reached the eastern end of the lake at about nine o'clock in the morn- 

 ing, and, after riding a short distance along its shore, admiring the beautiful 

 body of water as it lay spread out before me, its silvery surface unruffled 

 by even the faintest zephyr, at a convenient place I unsaddled and picketed 

 my horse, and, with tools and collecting bag, essayed to climb the bluff 

 that towered above me and the lake. The task proved a greater under- 

 taking than I had anticipated, but by perseverence and patience after 

 several hours of hard climbing, interrupted by frequent stops, to examine 

 and collect fossils from some particularly promising exposures, I arrived 

 at the summit. Never have I seen a more delightful and pleasing view 

 than that which greeted me. The morning, though calm, had been clouded 

 and altogether uninviting. As the day advanced, however, the clouds 

 vanished and the sun appeared, bathing the surrounding mountains with 

 its autumnal warmth, while, as from a highly polished mirror, its rays were 

 reflected from the surface of the lake that rested peacefully a mile beneath 

 me. Nor was the splendid view afforded by my commanding position 



