GENERAL PLANATION. 33 



sioually mingled with coarser stuff. In the special case of the Yung-ning 

 sandstone of Liau-tung, it is cross-bedded like a stream deposit from swift 

 and variable currents; usually it is evenly stratified after the manner of 

 deposits from quiet waters or on flood-plains. It is barren of fossils up to 

 100 feet, 30 meters, above the base, but above that horizon marine forms 

 are evident. 



Hence it is reasonable to infer that the zone of unconformity, compris- 

 ing the immediately subjacent rocks, the contact, and the directly super- 

 jacent strata, represents a coastal plain reduced through erosion and lateral 

 corrasion by streams to an even surface; covered during an early stage of 

 subsidence relatively to sea-level by alluvium, and buried beneath fine, ill- 

 assorted shore deposits of a shallow, rippling, advancing sea. Where the 

 waves removed the alluvium the marine strata are among the lowest; 

 where they did not, the bottom layers are of fluviatile origin. 



It is possible that such a coastal plain should be diversified by an 

 occasional hill of resistant rock, and hills of that kind may still survive if 

 preserved through burial in sediment. Where the strata have in a recent 

 geologic epoch been eroded from about them, they may again appear as 

 prominent features of the landscape. Such was von Richthofen's view 

 regarding the quartzite ridge of Ta-ku-shan and others like it. While grant- 

 ing the possibility of individual cases occurring, we do not agree to the 

 statement of the final sentence in the preceding quotation : "They constitute 

 the characteristic mountains of Shan-tung and Liau-tung." We consider 

 the present relief of those peninsulas to be a relatively very modern phenom- 

 enon, and hold that resurrected hills of the early Sinian epoch are few. No 

 case of the sort came under our observation. 



The preceding statements apply to the unconformity at the base of 

 the Sinian, wherever we saw it: in Shan-tung, Liau-tung, Shan-si, and 

 Hu-pe'i. Its character as a plane is uniform over a stretch of a thousand 

 miles, representing several hundred thousand square miles of contact. It 

 is a feature of southeastern Asia, from latitude 30 to 42 north and longi- 

 tude 108 to 124 east. 



Near Ta-tung-fu in northern Shan-si, von Richthofen observed an 

 occurrence of characteristic Sinian limestones, having at the base red, clayey, 

 and calcareous thin-bedded deposits, which rest unconformably on gneiss. 

 He remarks that the " Untersinisch," i. e., the Nan-k'ou limestones, are here 

 wanting. The occurrence is one of overlap of the Cambrian strata, to 

 which we restrict the term Sinian, beyond the pre-Cambrian, Nan-k'ou, 

 limestones or their littoral equivalents onto a much older pre-Cambrian 

 (Archean?) gneiss.* 



* China, vol. 11, p. 358. 



