LATER PROTEROZOIC. 9 



in curved and minutely contorted laminae of flint, the contortion of which 

 appears to be independent of local deformation of the strata. Similar 

 bands have been noticed in the Siyeh limestone of the Belt formation, Mon- 

 tana.* They are noted by Loczy as occurring in the Nan-shan sandstone 

 of Tibet. f Similar forms, described by Stose in Cambrian limestones 

 of the Appalachian Valley, are classed as Cryptozoan proliferum Hall.J 

 Whether the peculiar structures are in some cases mechanical or organic is 

 not known, but they have a long range from late Proterozoic to Ordovician. 

 They have not, however, been seen in the Sinian. Neither have the oolitic 

 and conglomeratic phases of the latter been observed in the Ta-yang. 



The thickness of the Ta-yang in a partial section measured by Black- 

 welder west of the type locality exceeded 1,200 feet, 360 meters, by an 

 unknown amount. Willis observed a section northwest of T'ang-hien, 

 Chi'-li, which, though interrupted by at least two normal faults, appeared 

 to include 6,000 feet, 1,800 meters, of the limestone. The thickness is, 

 no doubt, several thousand feet. 



At the base of the Ta-yang limestone is usually a thin stratum of 

 slate or phyllite, which rests in marked unconformity upon the T'ai-shan 

 complex (Archean). No doubt the limestone may occur in unconformity 

 on the Wu-t'ai schists, as does its probable equivalent, the Hu-t'o system, 

 but we did not observe any such instance. The occurrences we saw were 

 at points west of Pau-ting-fu, Chi'-li, and have been described in detail. || 



A contact of the Ta-yang limestone with strata of Sinian age was 

 observed at Nan-t'ang-me'i, Chi'-li (see vol. I, fig. 27, and atlas sheet F I). 

 A very heavy bed of residual chert pebbles, derived from the pre-Cambrian 

 limestone there, occurs beneath quartzite and black argillite, which are con- 

 formable to the overlying Sinian and which, though lithologically peculiar, 

 are believed to belong to that system. The body of residual chert is 

 regarded as an accumulation on the eroded surface of the Ta-yang, which 

 was therefore folded and exposed before the lowest Sinian stratum was 

 deposited. 



Having thus described the Ta-yang limestone and its relations as we 

 saw them, I give the following sections from von Richthofen, in which 

 he noted strata that closely resemble it in character and stratigraphic 

 position and which we consider to be its equivalents. These sections also 

 include the Sinian, namely, von Richthofen's Obersinisch, and the Ta- 

 yang equivalents are described by him as the Untersinisch. He did not 



* Stratigraphy and Structure of the Lewis and Livingston Ranges, B. Willis, Bull. G. S. A., vol. xm, 

 p. 305, 1902. 



t Reise des Grafen Szechenyi in Ostasien, vol. I, p. 553. 

 JChicago Journal of Geology, vol. xiv, pp. 210 and 217, 1906. 

 Fig. 27, vol. i, page 131. 

 II Vol. i, p. 130. 



