I,ATER PROTEROZOIC, NAN-K'OU TERRANE. II 



The close comparison practicable between the observations which 

 von Richthofen made in rapidly crossing the Nan-k'ou pass and the detailed 

 sections we were able to measure in Shan-tung bears testimony to the accu- 

 racy and painstaking character of his work. The differences are not greater 

 than might be expected in sections 300 miles apart, and all the character- 

 istic earmarks of the formations are noted by him in their appropriate 

 succession. Although he was not able to collect fossils, he observed their 

 occurrence at horizons elsewhere abundantly fossiliferous. That von Richt- 

 hofen did not see any unconformity between the Sinian and the strata 

 d, e, f, g, which we assign to a pre-Sinian system, is not surprising. He 

 remarks that the dip in the red strata (basal Sinian) was variable. The 

 limestones are very much alike in the two systems, and even one who is 

 looking for an unconformity may easily pass the contact in crossing a single 

 section en route to "distant night quarters which were difficult to reach." 

 Negative evidence of that kind has little or no weight. Nevertheless, it 

 is obvious that the strata in the Nan-k'ou pass are less closely folded than 

 in the vicinity of Si-ta-yang, where we observed the pre-Sinian rocks, and 

 it is possible that an unconformity of dip may not exist. But even if the 

 strata be conformable, it would still, in our judgment, be undesirable to 

 extend the term Sinian to the great body of siliceous limestones below the 

 Man-t'o shale, the first formation laid down in consequence of the trans- 

 gression with which the Sinian period opened. 



If the equivalency of the Ta-yang limestone with that exposed in the 

 Nan-k'ou pass be eventually established, it will be desirable to abandon 

 the term Ta-yang for Nan-k'ou as the name of the system. Nan-k'ou is 

 the locality where the strata were first distinguished; they are apparently 

 more completely represented there. The locality is at once well known 

 and accessible, it being on the highway from Peking to Kalgan. Believing 

 the strata to be equivalent, I regard Ta-yang as a local name that in 

 systematic discussion should give way to Nan-k'ou. Cherty limestones of 

 the Nan-k'ou terrane are described by von Richthofen as outcropping in 

 a ridge adjoining the Nan-k'ou range,* but the section is incomplete. 



In southern Chi-li, near "Hwo-lu-hsien," longitude 114 30', latitude 

 38+, a section of limestones is exposed in the " Hsi-p'ing-shan " moun- 

 tains bordering the Great Plain, which von Richthofen describes as follows 

 from above downward: 



Firm sandstone, white and gray. 

 Crystalline limestone. 



(Interruption.) 



Greenish gray, brightly colored, ringine. thin-bedded siliceous limestones; interbedded 

 with various sorts of strata. 



*China, vol. n, p. 343. 



