MARGIN OP THE RED BASIN. 85 



supposed to account for the sharp contact of the red shale on the Wu-shan 

 limestone, may be assumed to be of less duration than that represented by 

 marked unconformity of dip; and therefore the strata succeeding upon the 

 area of marine scour would probably be older than those transgressing upon 

 the area of subaerial erosion. The former might be late Paleozoic, as Girty 

 suggests. The latter probably range from early Mesozoic to Jurassic. 



The middle Yang-tz'i region, where the strata have been observed by 

 Pumpelly, von Richthofen, and ourselves, is continuous on the west with the 

 Red Basin of Ssi'-ch'uan. The next notable observations on the Paleozoic- 

 Mesozoic rocks relate to the northern margin of that basin near Kuan-yiian- 

 hien, in the region reached by von Richthofen, Loczy, and Obrutchov, and 

 already several times referred to. 



South of the section exposed by the Kia-ling-kiang across the folded 

 Paleozoics are strata which dip gently southward into the Red Basin. There 

 is a marked unconformity, above which the first formation is a massive 

 limestone. Von Richthofen regarded it as probably Permian or Triassic.* 

 Loczy describes the section observed by von Richthofen in nearly the same 

 terms, t and refers the limestone, which has a thickness of 1,400 feet, 400 

 meters, or more, likewise to Permian or Triassic. He, however, leaves the 

 possibility of a still younger age (Rhaetic) open. In certain thin-bedded, 

 light-colored, marly limestones, which are the uppermost strata of the folded 

 series beneath the undisturbed supposed Permian limestone, he collected 

 indistinct fossils, on which he comments as follows :J 



Among the materials which I collected there occur a cast which resembles Megalo- 

 donta, an Aviculopecten, as well as numerous examples of that little bivalve which we com- 

 monly designate by the indefinite name of Myacites. These forms permit us to suppose 

 that the marly clays and thin-bedded limestones which overlie the supposed Carboniferous*., 

 sandstone may be of Upper Carboniferous age, and that they perhaps are the southern 

 representatives of the North China supra-Carboniferous series. But the possibility is not "* 

 excluded that even Permian and Triassic may be included among these disturbed strata, 

 and that the evenly bedded limestone which occurs at the base of the middle Jurassic sand- 

 stones, in the Basin of Ssi'-ch'uan, may belong to the Rhsetic system. I found, in fact, 

 the traces of this system in the western margin of the Basin of Ssi'-ch'uan, as we shall see 

 further on. 



The observation to which Loczy refers in the preceding paragraph is 

 probably that which he records on pages 736 to 739. In an excursion in 

 the vicinity of Tschung-tjen he observed Triassic strata which were appar- 

 ently conformably bedded between two heavy limestones, both of which he 

 assigns to the Carboniferous. He explains the relations by a conformable 



* China, vol. n, p. 603. Quoted in full in this report, vol. I, p. 295. 

 t Reise des Grafen Sze'chenyi, vol. I, pp. 439-440. 

 \Ibid., vol. I, p. 441. 



