CHAPTEK XII. 



JURASSIC SYSTEM. 

 Namyau Series. 



Attention has already been drawn to the fact that there is no 

 evidence of a stratigraphical break between 

 formity V1 ° unC ° n the Napeng beds and those that succeed them, 

 the absence of the former at the base of the 

 overlying formation being accounted for by irregularities in the 

 limestone floor upon which both were laid down. The change in 

 the character of the deposits, which is well marked, seems to have 

 been caused by the circumstance that, as the sea encroached upon 

 the land, its shores in time extended up to the foot of the 

 highlands, composed of ancient crystalline and other more or less 

 siliceous rocks, which had surrounded the Devon-Carboniferous sea, 

 and that the sediment resulting from the degradation of these 

 older rocks was discharged directly into its waters and spread over 

 the sea floor. 



In the first instance, perhaps contemporaneously with the deposi- 

 tion of the Napeng beds, banks of coarse 



Conglomerates at base. , . . ' ~ . „ .. , ,, 



conglomerate, consisting of well rolled pebble 

 of the Plateau Limestone and of the mor«j ancient rocks, set 

 in a sandy calcareous matrix, were laid down ; but these are by 

 no means continuous, and perhaps merely mark the position of 

 beaches surrounding portions of the irregular limestone floor that 

 remained for a time above water, and they are confined entirely 

 to the base of the formation. Good examples of this conglomerate 

 are to be seen on the Nam-Tu, a short distance above Ta-ti ferry 

 (Loc. 7, F 2), on the trade route leading north from H .si paw, and at 

 Htengnoi lower down the river. As the sea deepened the material 

 deposited became fine-grained, sandy or argillaceous, and a formation, 

 consisting in the main of alternating beds of sandstones, shales and 

 clays, with very subordinate carbonaceous layers, was gradually 

 built up. It does not appear, however, that the water ever became 

 very deep, for the sandstone layers are often beautifully ripplr- 

 niarked. Examples of this structure may be seen in the deep 

 cuttings on the railway abovo Hsipaw, where the hills come down 

 to the banks of the Nam-Tu, 



