348 LA TOUCHE : GEOLOGY OF NORTHERN SHAN STATES. 



The nature of the oldest of the fossiliferous rocks that we find 

 deposited upon this ancient sea-floor enable 

 Conditions antecedent us to form some idea of the conditions that 



to deposition of fossili- . . t-iit i • 



ferous strata. immediately preceded the dawn of the his- 



torical period. Wherever they are exposed in 

 contact with the older rocks they contain no coarse material winch 

 would suggest the proximity of high land, but consist entirely of 

 fine grained sandy marls and limestones, such as would be accum- 

 ulated on the sea bottom either at a considerable distance from 

 land, or on a coast separated from the hills by a broad stretch of 

 alluvial plain. The conditions may in fact have been similar to 

 those now obtaining in the country surrounding the Bay of Bengal, 

 where a broad belt of low-lying ground, over which no pebbles or 

 coarse detritus can be found, intervenes between the coast and the 

 hills. Again, the great variation in the thickness of the oldest 

 fossiliferous strata, the lower Naungkangyi beds, — several hundred 

 feet in the western part of the Shan plateau being represented by 

 a band of only a few yards in thickness in the Eastern Ranges, — 

 may be due to the unevenness of the floor of this ancient sea ; 

 though it may of course be due to other causes, such as deficiency 

 of sedimentation in the eastern area, or to partial denudation in 

 later times. Taken together these characteristics,— the fineness of 

 the sediments and their variation in thickness, — seem to show that 

 the old land, before being submerged, had been worn down to a 

 peneplain but little raised above the sea level of that time ; and 

 that when submergence took place, the sea swept over a very 

 large area, in such a manner that the new coast line was situated 

 at a considerable distance from that portion of the sea-floor on 

 which the fine grained beds that now exist were deposited. 



The sequence of events, supposing that the Chaung-Magyi 

 rocks are the remains of ancient deltaic deposits, thrown into 

 folds and denuded before the deposition of the Naungkangyis, 

 might perhaps be compared with what would happen if the Pliocene 

 beds of the Arakan Yoma, wliich are evidently the deltaic deposits 

 of a great river formerly issuing from the Himalaya to the north, 

 thrown into a series of compressed folds, were planed down to 

 sea level and submerged by the waters of the Bay. Sands and 

 mud would be deposited upon heir edges, necessarily fine-grained 

 because the nearest hills, the Assam range and the edge of the 

 Shan plateau, which would form the new coast line, would lie at a 



