178 LA TOUCHE: GEOLOGY OF NORTHERN SHAN STATES. 



I have treated this fauna as distinct from that of the under- 

 Classificati n ty m S Silurian formations, both because it is 



evident, from a study of its affinities, as 

 shown in this list, that it marks a new phase in the conditions 

 prevailing in the Burmese region, and because some doubt exists 

 as to whether these beds should not be classed rather with the 

 overlying Plateau Limestone, which is certainly in part of Devonian 

 age, than with the strata of Silurian age already described. 



The reasons that have led me to place these beds in the Silurian 

 system are, not only the occurrence in them of graptolites, the 

 presence of which is looked upon, at least among English geologists, 

 as a kind of ' hall mark ' peculiar to that and older systems ; but 

 also a consideration of the general facies of the fauna they contain. 

 The great majority of the species are certainly of Silurian, — Wen- 

 lock or Ludlow,— types ; but the extraordinary profusion of the 

 annelid Tentaculites elegans, a characteristic lower Devonian species, 

 and the equally characteristic affinities of the few trilobites that 

 accompany it, might lead some geologists to argue that in this 

 region graptolites may have survived into Devonian times, and that 

 the beds should be classified accordingly. The stratigraphical 

 evidence is by no means in conflict with this view ; on the contrary, 

 there appears to be a perfectly gradual passage from the graptolite 

 beds into the overlying limestones. The case seems to bear a very 

 close resemblance to that of the relations of the Silurian and De- 

 vonian rocks in the classic area on the borders of Shropshire and 

 Herefordshire ; where we have a series of ' Passage beds ' containing, 

 on the one hand, graptolites, and, on the other, a euripterid and 

 cephalaspid fauna, whose affinities lie rather with that of the over- 

 lying Old Eed Sandstone. In that case the classification of the 

 ' Passage beds ' with the Silurian is generally accepted. For these 

 reasons I prefer to adopt what I may call the ' graptolite con- 

 vention,' for convenience of classification only ; knowing that if I 

 err in doing so, I err in good company. I therefore include the 

 Zebingyi beds in the Silurian system. 



As regards the affinities of the Zebingyi fauna, it has been shown 

 that the fossils from the formations hitherto dealt with, the Naung- 

 kangyi and Namhsim groups, belong mainly to types charac- 

 teristic of strata of similar age in Northern and Western Europe ; 



but in the beds now under consideration the 



Hereyinan type. , . - ., j- 



most important fossi'S possess a distinctly 



