CHARACTER OF MIDDLE SIMIAN. 41 



The black oolitic limestone, which commonly but irregularly occurs 

 in the green shale above the red Man-t'o, reached a maximum thickness, 

 as we observed it, of 550 feet, 165 meters, near the village of Ch'ang-hia,* 

 and we called it the Ch'ang-hia oolite. In consequence of its massive 

 character and vertical jointing it there forms imposing cliffs, and one does 

 not suspect that it may, in a short distance, thin out to a layer of vanish- 

 ing lenses. Such is, however, the case, as we found in the district north 

 of Sin-t'ai-hien, where a stratum 100 feet, 30 meters, thick gave out in 

 less than a mile. The color of the rock is due to the black oolites, with 

 which it is usually crowded. Blackwelder has described their peculiarities^ 

 and he finds that there is a series of forms ranging from true oolites, 

 which exhibit a nucleus and concentric banding, through grades of finer 

 to coarser crystalline texture, to a single crystal; and he concludes that all 

 the bodies had a common origin as oolites, which formed concentrically 

 around a nucleus. Some have remained but little altered and show the 

 original structure, while others have more or less completely crystallized. 

 Crystallization has progressed from a primary condition of many minute 

 crystals toward an ultimate development of a few or one large crystal. The 

 fossils of the Ch'ang-hia limestone are trilobites, brachiopods, etc., of Middle 

 Cambrian age. 



The middle portion of the Kiu-lung group is characterized by the 

 predominance of shale. In the vicinity of Ch'ang-hia a single stratum 150 

 feet, 45 meters, thick was so clearly distinct that we described it as a sep- 

 arate formation, the Ku-shan shale. In the Kiu-lung hills and adjacent 

 areas, however, no individual shale formation was distinguishable, the mass 

 of shale and limestone layers being on the whole thicker, but irregular. 



A special interest attaches to this member, since conglomeratic lime- 

 stones, such as have been described by Walcott as " intraformational 

 conglomerates," are of common occurrence in it. These peculiar rocks 

 consist of an earthy calcareous matrix, in which flat, pebble-like bits of 

 limestone are irregularly embedded. The pieces are commonly rounded, 

 but sometimes sharply broken ; they are fragments of thin limestone sheets, 

 which were broken up, washed, and rearranged during the formation of the 

 stratum in which they occur. Among the hypotheses that have been sug- 

 gested to account for these conglomerates, we are restricted to those which 

 regard the pebbles and the matrix as essentially contemporaneous. The 

 fact of unbroken conformity with the immediately underlying stratum, 

 which has been observed in every instance, excludes any hypothesis that 

 presupposes unconformity and erosion of older rocks. Identity of earthy 

 calcareous composition of pebble and matrix, and particularly identity of 



*Vol. i, Plate xiii. 

 f Ibid., p. 30. 



