294 THE CLIMATIC FACTOR AS ILLUSTRATED IN ARID AMERICA. 



"At the top of the tiUite, beneath a chff, is a well-exposed contact with the overlying lime- 

 stone. The tillite passes into a greenish shale, consisting of the same materials, including char- 

 acteristic pebbles, all rearranged by the water. This shale conglomerate is a,bout 2 feet thick and 

 grades into the overlying limestone, the basal layer of a great thickness of Sinian. 



"The facts clearly demonstrate the presence at this spot of a glacier which gave way to marine 

 waters and left a deposit of till that was slightly washed by waves before it was buried beneath 

 calcareous mud. * * * . , 



"Whether the Nan-t'ou glacier was an exceptional occurrence or a representative of an ex- 

 tensive system, only in degree affects the deduction that the temperature of early Sinian time was 

 low. Glaciation in latitude 31° near sea-level presents, it is true, a problem which refrigeration 

 alonewill not solve, especially asnotracesof contemporaneous glaciers have been foundfarther north; 

 but there can be no doubt that it signifies severe cold throughout northern Asia" (1909: 39-40). 



Professor J. P. Iddings, while on a geologic tour in China, visited the Nan-t'ou region in October 

 1909, and from him has been received the following description of the tillites: 



"The tillite is extensive and quite persistent in character, though somewhat variable in thick- 

 ness. It is interbedded with the basal sandstone resting on the granite-gneiss, and I did not find 

 it in contact with the granite. I first examined the locality discovered by Willis and Blackwelder. 

 * * * The formation extends for 3 or 4 miles back from the Yangtsze to the north along 

 the base of the cliff of limestone. Some distance back from the river, I crossed the branch creek 

 that enters the Yangtsze at Nantou. The branch is in granite which rises in the east slope about 

 400 feet. Here occurs the base of the conglomeratic red sandstone, dipping 5° SE., strike N. 40" 

 E. (magnetic). The top of the sandstone is 200 feet higher. The upper .50 feet contam white 

 layers, alternating with red. Near the base of the tillite there are some thin clay layers in the 

 sandstone, and in the base of the tillite is some red sandy rock. The two appear to mix and to 

 grade into one another. Similar mixture and gradation were observed in numerous places farther 

 north. The tiUite at the location on the branch creek is green and of the same aspect as in other 

 places visited. It contains many boulders and pebbles in the middle portion; not so many in the 

 basal or in the uppermost portions. There were no signs of bedding, and no intercalated stratum 

 of sandstone, as in a case south of Huang-Ling-Miao noted later. The tillite is about 150 feet thick 

 and is overlain by limestone, the bottom layer of which is more massive than the higher layers. 



" Traveling northward across spurs that set forth from the cliffs east of a branch stream, the 

 base of the sedimentary rocks rises gradually as far as I went, about 3. .5 miles in a direct line 

 from Yangtsze River. I observed a fault cutting across the spurs shifting the exposures of 

 tillite, the trend of the fault being about with the strike (about N. 45° E.), and the hade very 

 steep, about 75°, apparently to the west, though not distinct. The strata and the granite on the 

 west were raised with respect to the same on the east, the displacement being about 100 feet. 

 The result is apparent variableness in the thickness of the tiUite bed, and to cause it in places to 

 p.^^wt against the granite. -c i i 



" Crossing to south side of Yangtsze opposite Nantou, I followed the base of the stratified rocks 

 westward as they rose above the granite, and occasionally saw exposures of tillite. Back of 

 Huang-Ling-Miao, granite extends up spurs to 1,700 feet above the river; then follow about 300 

 feet of massive strata of red sandstone, which is immediately overlain by tillite, the lower 5 

 feet of tillite having a layer of sandstone blended with it. There are few boulders in the lowest 

 part, but more higher up. The pebbles are of granite, gneiss, porphyry, slate, limestone, flint, 

 and quartz. The lower portion of tillite is yellow and clayey, the upper portion is green and 

 indurated, as at Tungling. About 200 feet from the base is a massive stratum of red sandstone, 

 about 6 feet thick, having the same strike and dip as the strata above and below it. Above this 

 there is tillite for 200 feet more, making the thickness of the tiUite in this locality between 400 and 

 500 feet. The overlying limestone is somewhat brecciated at its base for 6 inches to a foot, and 

 then becomes massive, with some contortions of the lines of bedding, for a thickness of 3 or 4 

 feet. Then follows thinly bedded to fissile arenaceous limestone, and layers of arenaceous shales 

 quite uniform in character up to about 2,700 feet above the river. The strike of the strata is 

 N. 45° E., dip 10° SE. No trace of fossils was seen, though there were fine exposures of strata 

 and talus.' The cliffs rise to about 3,500 feet above the river. The area of granite hills north of 

 Yangtsze River was well seen from a high spur south of the river. The sedimentary strata were 

 seen to arch in a dome around flanks of the granite hills to west and north and to east and north. 

 South of the river sedimentary strata appear to extend in an arch around to Tungling, at the 

 lower entrance to Lukan gorge on the west side of the granite arch. 



"At Tungling the tillite is seen on both sides of Yangtsze River, near the shores. On the north 

 side, in a bluff near the landing, it is about 300 feet thick. The tiUite here overhes red basal 



