26 RESEARCH IN CHINA. 



and subsequent prolonged continental phase, or marine transgression. The 

 latter is more probable, but we can not on present evidence exclude the 

 possibility that the upper Wu-t'ai strata accumulated subaerially on a low- 

 lying land. Confining our attention for the moment to the lower series, 

 which ranges from quartzose argillaceous to calcareous, we recognize a suc- 

 cession of rocks which, though much older, resemble the Sinian (Cambro- 

 Ordovician) terrane. At the base are the weathered, oxidized products of 

 subaerial rock decay, such as, in consequence of exposure above the plane 

 of gradation, are transported by streams and delivered to the sea. Toward 

 the top are the finer, finally chiefly calcareous sediments, which result from 

 the topographic and climatic conditions that follow from prolonged fixed 

 relations of land and sea. The unconformity indicates an interruption of 

 those relations which, if the overlap of the next later strata on the Archean 

 be as great as we suppose, was a. very notable interruption. The upper 

 series represents ultimately renewed erosion, transportation, and deposition. 

 The Wu-t'ai deposits are several thousand feet thick. They are at least 

 equal to the Cambro-Ordovician in duration of time and altogether may 

 equal most of the Paleozoic. The nature and volume and sequence of 

 sediments correspond with those which represent epeirogenic movements 

 and static conditions of later periods; they evidently indicate equivalent 

 movements and conditions for those early times. 



The Wu-t'ai strata were folded and intruded by igneous rocks, and the 

 whole mass was rendered schistose before the next succeeding formation 

 was laid down in the typical district. The igneous rocks became gneisses; 

 i the heterogeneous strata became biotite, muscovite, and chlorite schists; 

 and the limestones changed to marbles, with the development of garnet, 

 staurolite, and other minerals from the shaly beds. Metamorphism was 

 preceded by or associated with folding and thrusting into isoclinal struc- 

 tures. The phenomena compare in intensity and volume of rocks affected 

 with the effects shown by the Paleozoics of the Han region, China, or of 

 the Sierra Nevada, California, as a result of deformation during the Permo- 

 Mesozoic. 



Thus we see that the Wu-t'ai region passed through an epoch of intense 

 orogenic activity at the close of the Wu-t'ai period of the Proterozoic era. 



In other districts than that of the Wu-t'ai-shan, Shan-si, where strata 

 are identified by lithologic character as being probably of Wu-t'ai age, the 

 structural facts are less well known. In the Ts'in-ling-shan, Shen-si, chlo- 

 ritic schists with some limestone and quartzite occur unconformably beneath 

 Paleozoic strata, from which they are markedly distinguished by greater 

 metamorphism. The suggested events of deposition and orogenic disturb- 

 ance are comparable in time and character with those of the typical region. 



