ORDOVICIAN SYSTEM : NAUNGKANGYI STAGE. 



113 



greater ; and as so many of these undetermined fossils are trilobites, 

 I am in great hopes that with their helj), and with that of the 

 brachiopoda, it may be possible in the future to work out the true 

 palseontological sequence, when the country is more opened up. But 

 at present the attempt to make more than the broadest divisions, 

 as I have done on lithological and stratigraphical grounds alone, 

 would be hopeless, so far as the Shan States themselves as a whole 

 are concerned ; and I can do no more than suggest, as Mr. Cowper 

 Reed has already done, in what way this formation is related to 

 the Ordovician rocks of other countries. 



The difficulty of determining the horizon of each exposure with 

 . j respect to the whole series is enhanced by 



the fact that it is seldom that the fauna of 

 any one locality is strictly comparable with that of another, but 

 appears to depend upon purely local conditions of environment, 

 as in the case of the Cystidean beds of Sedaw. The brachiopods. 

 for instance, are most commonly found in calcareous sandy beds, 

 the cystideans and trilobites in argillaceous shales ; and the latter 

 are so homogeneous in character over large areas that the litho- 

 logical appearance of the rock gives no clue to the horizon of any 

 particular outcrop. The sandy texture of the brachiopod beds, 

 and the fact that when the remains of trilobites do occur in them 

 (and they are often numerous and of large size, indicating indivi- 

 duals at least 4 or 5 inches across), they generally consist of single 

 thoracic segments or fragments of a carapace, leads me to suppose that 

 these beds were laid down on the shallower portions of the sea 

 floor, where strong currents prevailed. If this was the case they 

 would naturally be of a lenticular form, and not continuous over 

 large areas. The bands of limestone also, which occur here and 

 there among the shaly beds, seem to have been accumulated under 

 similar conditions. They are to a great extent composed of the 

 ossicles of crinoids, and are in the main what may be called a 

 consolidated crinoid sand. Judging from the profusion of these 

 ossicles in the rock, and of fragments of crinoid stems in the 

 ' purple band,' there must have been an exceedingly rich crinoid 

 fauna in the Ordovician seas of this region, of which these ossicles 

 are the only traces that remain. 



The nearest region to which we may look for representatives 



_. . . . of <his scries of rocks, leaving out of account 



Himalayan equivalents. ,, 



lor (he preNcnl the sniiill patches whrch are 



