AN UNCONFORMITY BY EROSION. 67 



PRE-CARBON1FEROUS UNCONFORMITY. 



Throughout northeastern China, in the provinces of Chi-li, Shan-si, 

 Shan-tung, and Ho-nan, there is an unconformity which brings the Ordo- 

 vician in contact with the Carboniferous. Wherever it has been seen the 

 underlying terrane consists of the upper Sinian (lower Ordovician) lime- 

 stone; whereas the overlying strata are shales which lie a hundred feet or 

 so below beds that carry upper Carboniferous fossils, either marine shells 

 or plant remains. The hiatus appears, therefore, to represent later Ordovi- 

 cian, Silurian, Devonian, and lower Carboniferous times. 



Local observations all agree that the Ordovician and Carboniferous 

 strata are strictly conformable ; so closely parallel are they that von Richt- 

 hofen, who repeatedly saw the contact, assumed that they formed an 

 unbroken sequence, and characterized the Sinian limestone as Kohlenkalk. 

 He did not find any of the sparsely distributed fossils, by which its age has 

 since been determined by Lorenz and ourselves, and his error is one which 

 sprang naturally from the fact that he had previously observed a massive 

 Carboniferous limestone in South China. It follows from the conformity 

 of dip over several hundred square miles that the region in question was not 

 subjected to disturbing influences during the periods represented. The 

 Sinian strata were not folded; neither, during all this time, were they raised 

 to an elevation at which they might have been deeply eroded. 



Apart from the fact that the strata above and below the plane of 

 unconformity are identified by fossils and the existence of a hiatus is thus 

 proved, the contact itself shows evidences of erosion. The Sinian limestone 

 is deeply fissured and cavernous. The cavities show waterworn or corroded 

 surfaces, commonly found in limestones exposed to meteoric waters. These 

 cavities are filled with bright-colored clays, which owe their varied hues to 

 the oxidation and hydration of the iron which they contain. Bog-iron ore, 

 sufficient in quantity to be mined, and calcareous tufa are found at the 

 contacts. 



The significance of these facts has been discussed in connection with the 

 consideration of post-Sinian diastrophism. For detailed descriptions of the 

 unconformity as we saw it, reference may be made to volume i, pages 48 

 and 147. In describing the coal-field of Po-shan in northern Shan-tung, 

 von Richthofen* states with reference to the Kohlenkalk (Sinian lime- 

 stone) that he found no fossils, but noted that in contrast to similar lime- 

 stones in other regions it contained no chert. This distinction is one in 

 which the Sinian differs from the Carboniferous limestone of southern 

 China. 



*China, Vol. 11, p. 203. 



