SILURIAN SYSTEM : ZEBINGYI STAGE. 



181 



is of middle Devonian age, since it contains Orthothetcs umhraculum 

 Schloth., Atrypa aspera Schloth., and Cyathophi/llutn sp. 1 The 

 Muth quartzite has yielded no fossils, but it is by no means 

 unlikely that fossiliferous beds corresponding to it in age may 

 occur further to the north, in the little known districts north of 

 the Tibetan Plateau, where traces of the Hercynian fauna have 

 been found. 2 



A submergence of the northern part of the barrier that I sup- 

 pose to have existed during Ordovician and 



First symptoms of <-,., . ,. , i ,1 



Devonian transgression Silurian times between our area and the 



southern branch of the ' Tethys ' may have 

 opened up a connection with the northern portion of that sea. 

 However that may be, it seems certain that we have, in the Her- 

 cynian fauna of the Zebingyi beds, the first indication in South- 

 Eastern Asia of those great changes in the distribution of sea and 

 land which, as we shall find later on, brought a true middle Dev- 

 onian fauna into Burma, and culminated in a wide spread trans- 

 gression of the Permo-Carboniferous ocean over those truf.ts of 

 Asia lying to the north of Gondwana-!and. 



1 H. H. Hayden, Geology of Spiti ; M e.nr irs, Geol. Snrv. Iwl., Vol XXXVI, pt. 1, 

 p. 34. 



2 A. de Lapparent, Traite de Geologic 5tli Edn. p. 849, 



