ORDOVICIAN WARPING. 49 



laceous, but gradually become more and more siliceous till they pass up again into quartz- 

 itcs. This alternation continues with great regularity for many hundred feet. Towards 

 the top of the scries the argillaceous beds give place to light-colored siliceous slates and 

 thin-bedded flaggy quartzites, with bands of red and pink dolomite, which latter gradually 

 increases in frequency and thickness till it becomes the predominant rock. These beds 

 constitute the oldest fossiliferous series hitherto found in Spiti. 



After the statement of a detailed section, which comprises 1,188 feet, 

 371 meters, of strata, there follows the account of the fossils. Near the base 

 of the section, in a hard calcareous and micaceous quartzite, occur numerous 

 valves of a small brachiopod resembling Lingulella, with which are associated 

 indeterminate fragments of the head shields of a trilobite. About 400 feet, 

 1 20 meters, higher, trilobite remains are again abundant but poorly pre- 

 served. One hundred and sixty feet, 48 meters, still higher up, large num- 

 bers of specimens were collected in a very fair state of preservation. They 

 are said to consist chiefly of species of Ptychoparia, Cor da, and allied genera. 

 A hundred feet, 30 meters, higher Ptychoparia is still found and with it large 

 numbers of fragments of Olenus sp. and Dikelocephalus sp. About 90 feet, 

 27 meters, still higher occur the uppermost determinable fossils, among 

 which Ptychoparia is rare and Olenus common. Although the collections 

 which are thus briefly described had not been studied, the forms recognized 

 are considered sufficient to warrant the inference that the fossiliferous beds 

 are of Upper, possibly also of Middle, Cambrian age. 



POST-S1NIAN DIASTROPHISM. 



Sinian strata are commonly parallel in attitude with late Paleozoic 

 strata, where any such are present. The areas in which the sequence is 

 apparently immediate and sedimentation was continuous are limited, so 

 far as we know, to Central China; those strata that immediately succeed 

 are distinctly terrigenous sediments, which contrast decidedly with the 

 underlying marine limestones and represent a revival of erosion. Those 

 areas over which an unconformity of erosion without discordance exists 

 are extensive and comprise the Paleozoic of North China. 



From these facts it follows that diastrophism at the close of the Sinian 

 time involved broad epeirogenic changes, without marked orogenic disturb- 

 ances, within the provinces of eastern Asia. 



An exact date of the movement can not be inferred in the region of 

 unconformity by erosion, for it is impossible to determine what strata may 

 have been removed from the latest which are there present beneath the 

 unconformity. The latest remaining are lower Ordovician ; they are over- 

 lain by upper Carboniferous; and it is possible that Silurian, Devonian, or 

 lower Carboniferous deposits may have been spread over the area. It 



