THE GEOLOGIC FORMATIONS. 31 



Since Willis wrote the above in 1907, I have completed my study of the 

 relations of the Cambrian and pre-Cambrian in North America and have 

 concluded that the pre-Cambrian unconformity is universal in all known 

 localities of Cambrian sedimentation and that the depressions in which the 

 pre-Cambrian sediments were deposited were epicontinental, mainly non- 

 marine, and in no way connected directly with the subsequent Cambrian 

 sedimentation. [Walcott, 19106, pp. 2-3.] 



THE GEOLOGIC FORMATIONS. 



LOWER SIMIAN. 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 limestone. The thickness 

 varies from 350 to 500 feet (105 to 150 meters). The basal layers occa- 

 sionally 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 [1907, p. 38], 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 fav- 

 ored 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. [Willis, 1907, pp. 38-39.] 



The geological conditions thus briefly outlined clearly indicate that the 

 Man-t'o formation was the first deposit made over a wide area by the slowly 

 transgressing Cambrian sea. This area is outlined by Willis on his map of 

 "Southern Asia during the Sinian Period" [1907, plate 4]. 



MIDDLE SINIAN, KIU-LUNG GROUP. 



Willis describes this group in the following words: 



The Kiu-lung group of Shan-tung is a succession of limestones and shales which imme- 

 diately follows the Man-t'o formation. Transition beds connect the two. Shale is a 

 common rock in both, but in the Man-t'o it is red, whereas in the Kiu-lung it is green. 

 Limestone is thin-bedded and subordinate in the former; in the latter it is usually massive 



