1 8 RESEARCH IN CHINA. 



He describes the probable Wu-t'ai rocks thus: 



South of Twi-tsze-shang, gneiss and granite give way to a series of rocks which are 

 characterized by green color, and when the component minerals are macroscopically recog- 

 nizable consist of abundant hornblende or chlorite, or of both minerals, and exhibit great 

 petrographic variety. Predominant are rocks composed of reddish feldspar, blackish 

 green hornblende, and dark scales of chlorite. The last often occurs in irregular, some- 

 times sharply fringed spots, with hornblende, which lie in a ground-mass composed essen- 

 tially of feldspar. The chlorite then occurs next to the hornblende in such manner that one 

 is inclined to consider it an alteration product of the latter. Dikes of granite, pegmatite, 

 and quartz are common, especially in the northern zone. With reference to the arrange- 

 ment of the constituents, as well as with regard to their distinct separation, the rocks vary 

 greatly. Occasionally they are massive without recognizable parallel structure, and they 

 then have in some places the character of serpentine, the feldspar being subordinate. 

 More often the magnesium minerals are arranged in parallel surfaces, sometimes only 

 partially, as is the case with mica in gneiss-granite ; otherwise, however, so regularly that 

 more or less nearly perfect hornblende and chlorite schists are produced. 



With the first steps on this formation I was reminded of the Wu-t'ai schists of northern 

 Shan-si. Shortly there followed the typical members of that formation, as a very thick 

 sequence of green, partially schistose rocks, in which none of the constituent minerals are 

 macroscopically recognizable. The entire system of schists has, as a whole as well as in 

 its members, the constant strike of west 12 north, east 12 south. The dip is uniformly 

 south, mostly at an angle of 50 to 70, occasionally less steep. * * * 



Before reaching Tsau-liang-yi other rocks are seen in great numbers in float from the 

 eastern ravines. Predominant among them are dense, quartzitic rocks, whose fracture 

 planes gleam with innumerable little feldspar crystals. These are probably altered clayey 

 sandstone. Therewith occur conglomerates of rounded quartz, in a matrix which partly 

 corresponds to the above-described rock, is partly purely quartzitic, and has a reddish to 

 dark-violet color. As I was unable to find these rocks in place I can not say whether they 

 correspond to the sandstones and conglomerates which occur in the lower part of the 

 Wu-t'ai formation south of the temples of Wu-t'ai-shan, or whether they belong to the 

 coal-bearing strata which are presently to be described. 



It will be observed that the pre-Sinian rocks are more extensively 

 developed in the western section seen by von Richthofen than in the one 

 observed by our expedition. We did not find the zone which is described 

 by him as Archean gneiss and granite, and the belt of Wu-t'ai schists is 

 but 5.5 miles, 9 kilometers, wide, whereas that in his section is 20 miles, 32 

 kilometers, across. There is, indeed, little reason to suppose that the two 

 occurrences are one and the same zone. The strike in von Richthofen's 

 section, east 12 south, if extended, carries the belt which he saw at least 

 12.5 miles, 20 kilometers, south of that which we observed. This direction 

 appears to be the trend of axes in the range, and it is probable that there 

 are subparallel belts on distinct folds. If so, the eastern zone, extended 

 northwestward, lies beneath the Wei' valley, and the western, extended 

 southeastward, ends before it reaches our route. We crossed an anticline 

 in Paleozoic strata about in its line of strike. 



