NO. I CAMBRIAN FAUNAS OF EASTERN ASIA 39 



were epicontinental, mainly non-marine, and in no way connected 

 directly with the subsequent Cambrian sedimentation/ 



THE GEOLOGIC FORMATIONS 

 Lower Sinian, Man-t'o Shale 



The basal formation, the Man-t'o, is a red shale that passes often 

 into red or chocolate-brown shaly sandstone, and this is interbedded 

 with thin, sometimes persistent, layers of gray, cream-colored lime- 

 stone. The thickness varies from 350 to 500 feet (105 to 150 

 meters). The basal layers occasionally show local conglomerates. 

 The calcareous layers of the Man-t'o occur occasionally near the base, 

 persistently at horizons 100 to 150 feet (30 to 45 meters) higher up, 

 and again less commonly near the top, which is often sandy. The 

 transition into the overlying limestone of the Kiu-lung group is 

 formed of interbedded brown shales and gray limestones. 



The interbedding of the shale and limestone is irregular. It is 

 apparent that local conditions were unlike in adjacent waters at any 

 one time and varied in unlike manner from time to time, but red 

 sediment from the land or calcareous sediment from the sea was 

 deposited at any time, as stated by Willis,' who also says : 



One may form a concept of the conditions somewhat as follows : Along 

 . the flat, red shore of the Man-t'o sea, bars and islands formed where streams 

 emptied, and shut off the mud-carrying currents from intermediate stretches 

 of coast. More or less extensive lagoons were thus produced and within these 

 the waters were clear. Being partly closed and shallow, they were relatively 

 warm and liable to maximum evaporation. Rippling of the surface favored 

 precipitation of lime carbonate by agitation. Warmth and protection invited 

 organic life, both plant and animal, which probably occupied the lagoons in 

 low forms that did not become fossil before trilobites, the earliest that have 

 been preserved, discovered the habitat. 



The description of the Man-t'o formation has thus far dealt with it as it 

 is developed in northern China? The red mud does not occur in the south on 

 the Yang-tzi-kiang, where we saw the base of the Sinian, but the strata 

 which we suppose to be equivalent are thin-bedded gray limestones which rest 

 on a well-defined glacial till.'' 



The geological conditions thus briefly outlined clearly indicate 

 that the Man-t'o formation was the first deposit made over a wide 



'Walcott, C. D. Smithsonian Misc. Coll., Vol. 57, Cambrian Geology and 

 Paleontology, No. i, 1910, Abrupt appearance of the Cambrian fauna on the 

 North American continent, pp. 2-3. 



* Willis, Bailey. Research in China, Pub. No. 54, Carnegie Institution of 

 Washington, Vol. 2, 1907, Systematic geology, p. 38. 



' Idem, pp. 38-39. 



