286 LA TOUCH E: GEOLOGY OF NORTHERN SHAX STATES. 



named on account of the existence close to it of a very rich 

 fossiliferous deposit, about nine miles to the east of Pyaung- 

 gaung railway station. Since then other outlying patches of the 

 shales have been found, two of them far to the east on the south- 

 ern flanks of the Loi-len range (Loc. 24, I 1, Loc. 25, J 1), and 

 a third to the north, too small to be marked on the map, near 

 Man Sam (F 1), on the trade route leading north from Hsipaw. 

 I have already pointed out (ante, p. 262) that the discovery of 

 Fusulina in some of the limestones in the valley of the Nam-Tu 

 near Htengnoi makes it doubtful whether the whole of the area 

 coloured on the map as Napeng beds to the south of that place 

 really belongs to this formation or not. 



The occurrence of these beds at Man Sam is of special interest, 



as it is the only instance yet found in which 

 beds! kti0n t0 ° verlyiug the Napeng shales are associated with the 



overlying formation ; though even here the section 

 is so obscure that their exact relations could not be ascertained, in 

 spite of an attempt made to expose them by excavation. It is, how- 

 ever improbable that any considerable break took place between the 

 deposition of the Napeng and Namyau beds, and the general 

 absence of the former along the boundary separating the latter from 

 the Plateau Limestone must be explained on other grounds than 

 partial denudation of a continuous formation. 



If we consider the conditions that probably prevailed when the 



sea again invaded this area, after the Triassic 

 ^Conditions of deposi- j ^ & gimple explanation of 



the facts observed will appear. We have a wide 

 expanse of coral reefs, raised for a period to a sufficient height above 

 sea level to be exposed to denuding agents and worn into ridges and 

 hollows, many of the latter perhaps cup-shaped depressions similar to 

 those which are being formed at the present day. If an irregular 

 surface of this kind were gradually covered by the waters of the 

 sea, so as to be just awash, it would be natural that the sediment, 

 most of it of an exceedingly fine character derived from the residue 

 left by the degradation of the limestones still above water, would silt 

 up the hollows, some of which might be at times cut off from 

 communication with the open sea or from each other. In this man- 

 ner the absence of these beds in positions where one would expect 

 to find them is accounted for, without having to suppose tha f a 

 temporary reversal of the downward movement, with consequent 



