68 



NATURE 



[Nov. 20, 1879 



a little while on the flanks of the great mountain range 

 that formed the colossal bulwarks of the parks of Colorado. 

 As seen from the prairies they rose in a picturesque line 

 of peaks, visible in the clear atmosphere of these regions 

 at an incredible distance, and looking at first like mere 

 low islets, the greater part of their bulk being still hidden 

 beneath the sea-like surface of the prairie. Composed of 

 crystalline rocks these crests had been pushed as a great 

 wedge through the cretaceous and tertiary rocks of the 

 prairies, and had carried those rocks up with them in a 

 grandly picturesque curve along their flanks. An excur- 

 sion into some of the gorges or canons by which the 

 flanks of these mountains are trenched, brought to 

 notice some interesting facts connected with the surface 

 erosion of the district. He then found the source of the 

 pink felspar sand of the prairie ; it had been borne down 

 from this region, where great masses of pink granite, grey 

 gneiss, and other crystalline rocks formed the core of the 

 mountains, and were visibly crumbling into the same kind 

 of pink sand and gravel. He found that the mountains 

 had been covered with glaciers which had gone out into 

 the plains and shed their huge horse-shoe shaped 

 moraines where now everything was parched and barren. 



Having crossed the watershed of the continent, he 

 struck westward into the Uintah Mountains, one of the 

 few ranges in that region that had an east and west 

 direction. This range had been visited by Hayden, had 

 been mapped by Clarence King and his associates, and 

 its eastern end had been carefully examined by Powell. 

 It formed one of the most remarkable elevations in North 

 America. Unlike the other mountainous high grounds it 

 possessed no great central core of crystalline azoic rocks, 

 but consisted of a vast flattened dome of red sandstones, 

 dipping steeply down beneath mesozoic rocks on either 

 flank. The precise geological age of these sandstones 

 had been a matter of dispute. King had regarded them 

 as carboniferous. In their lithological characters they 

 much resemble some of the old red sandstone of Scot- 

 land, while some of the more compact portions, recalled 

 the red Cambrian sandstones of Applecross and Assynt. 

 One feature of surpassing interest in the Uintah Moun- 

 tains was the evidence of enormous denudation, continued 

 through a protracted cycle of geological time. The 

 horizontality of the strata along the central parts of the 

 range was such that terrace above terrace could be traced 

 by the eye for miles around any commanding peak. The 

 rocks there had escaped crumpling and fracture to a re- 

 markable degree. It could therefore be seen that the 

 deep gullies and clefts, the yawning precipices and 

 canons, the wide corries and vast amphitheatres by which 

 the surface was so broken up had been produced not by 

 underground disturbances but by erosion at the surface. 

 Most of this tremendous denudation had doubtless been 

 effected by ordinary atmospheric action. The speaker de- 

 scribed the disintegrating effects of the remarkable daily 

 vicissitudes of temperature in this region, the action of 

 wind, as well as of melting snow, and occasional torrents 

 of rain. But he showed that the mountains had also 

 nourished large glaciers, and that these, filling up the 

 main valleys had protruded into the plains beyond. They 

 had left behind them numerous lake basins, some ground 

 out of the horizontal sandstones, others dammed up by 

 fallen moraine debris. 



Striking into one of the valleys, he found it crossed by 

 beautiful horse-shoe moraines that had once formed a 

 succession of lakes, of which the sites were now occupied 

 by meadows. In these and other high grounds, however, 

 it was the beaver, which, by its dams, converted even the 

 small streams into a succession of shallow lakes. In most 

 of these valleys there were hundreds of acres of bog land 

 entirely due to the damming of the water by the beavers. 

 The Uintah Mountains were flanked by ranges of low and 

 sometimes fantastic hills, mesas or terraces, and isolated 

 buttcs or outliers, included under the general term 



" mauvaises terres " or " bad lands." This designation 

 referred to the fact that the ground was everywhere 

 crumbling down under the action, of the weather, 

 and nothing would grow upon it. The strata of these 

 bad lands were flat or nearly so, and showed their lines 

 of bedding with singular precision along the faces of the 

 crumbling cliffs and slopes. They had an arid and 

 almost ghastly aspect, grey, verdigris green and yellow, 

 as they rose out of the sandy wastes at their base. It was 

 from these strata that Prof. Marsh had obtained some 

 of the marvellous reptilian and other forms which 

 he had described from the eocene and cretaceous rocks of 

 the West. Prof. Geikie narrated a ride through the 

 forest lands of the mountains, and gave an account of how 

 the party, benighted away from camp, had to pass the 

 night without food on the bare ground, and how the forest 

 around them caught fire. 



The journey to the Yellowstone region was one of great 

 tediousness and discomfort. Having letters from the 

 Secretary of War and the Quartermaster-General of the 

 United States, the party received every attention at Fort 

 Ellis, where a pleasant day or two were spent, examining 

 with the officers of the garrison the geology of the district. 

 From this point the journey was performed on horseback 

 and with a pack train of mules, the officer in command 

 at Fort Ellis having furnished an outfit, scout and escort. 

 The Professor gave a narrative of the traverse of the 

 Yellowstone country, dwelling specially on the evidences 

 of former successive periods of volcanic eruption, and on 

 the proofs of intense glaciation to be observed in the 

 ascent of the valley of the Yellowstone River. The tokens 

 of a long period of volanic activity contemporaneous with 

 the operations of the river, resembled those of Auvergne, 

 but on a much larger scale. The mountains around con- 

 sisted mainly of crystalline rocks such as gneiss, schist, 

 and granite. The volcanic action appeared to have been 

 chiefly confined to the valley. Sheet after sheet of lava 

 had been poured out, and these, one after another, had 

 been cut through by the river. The edges of some of the 

 lava plateaux could now be seen crowning the summits of 

 steep slopes or even cliffs far above the level of the stream 

 below. So great had been the general erosion that 

 no distinct craters remained now visible. But what ap- 

 peared to be the stumps of some of these, filled up with a 

 coarse volcanic agglomerate, were here and there 

 observed. The lavas offered a vast and tempting field of 

 investigation, presenting as they did a great number of 

 petrographical varieties. Some of the obsidians were 

 particularly interesting in their pumiceous and spher- 

 ulitic characters. The Grand Canon of the Yellowstone, 

 cut out of these volcanic masses, was described as 

 perhaps the most marvellous piece of mineral colour any- 

 where to be seen in the world. It had been cut out of 

 tuffs and lavas, showing sulphur yellow, verdigris or 

 emerald, green, vermilion, crimson, and orange tints, so 

 marvellous that, if transferred to paper or canvas they 

 would be pronounced incredible and impossible ; the lec- 

 turer said he had spent a day in making a careful water 

 colour ,study of this canon, but he hardly expected to gel 

 any of his friends to believe in the truthfulness of his 

 colouring. 



During the ascent of -the Yellowstone Valley the evi- 

 dence of former extensive glaciation was abundant and 

 conclusive. The party had hardly been in the ralley a 

 quarter of an hour when they descried, not far above the 

 upper end of the first or lowest canon, a large block 

 among some mounds in the centre of the plain. This 

 proved to be an erratic of coarse granitoid gneiss, lying 

 among many others of smaller size. The mounds, mani- 

 festly moraines, curved in vast crescents across the broad 

 plain of the Yellowstone. Further] mounds and scattered 

 blocks were noted in the ascent of this great expansion 

 of the valley. On reaching the entrance of the second 

 canon, the Professor found it most exquisitely glaciated 



