\iC) DTFNF.l? : TKTAS OF TTTK ITTMALA VAS; . 
than the large percentage of species, which are nearly allied to 
European forms. 
Many important types point to the carnic stage and are indicative 
of a homotaxis with the Alpine zone of Tropit.es stibbiillatus. But a 
second faunistic element pointing to the noric stage is almost equally 
distributed in the Tropites limestone. Not less than 49 species of 
ammonites are either identical or very closely allied with specie.* from 
the noric Hallstatt limestone or (13) from the Halorites beds. A. v. 
Kraft't was the first author to notice this strange assemblage of carnic 
and noric types in one single bed of limestone only three feet 
thick 
It might be suggested that this fauna marks a tran;itional stage 
bridging over the faunistic hiatus, which exists between the carnic and 
noric stages of the Eastern Alps. But Diener remarks that such 
faunistic elements as might be regarded as transitional forms con- 
necting the two faunae are missing, and that the species present in 
variably show distinctly carnic or noric affinities. He consequently 
denies the possibility of considering the Tropites limestone as a true 
passage bed from the carnic to the noric stage. 
He further insists on the remarkable similarity of the strong admix- 
ture of carnic and noric types in the Tropites limestone of Byans with 
the remarkable association of Kelloway and Oxford ammonites in the 
Jurassic oolites of Balin (Galciia), which has been explained by Neumayr 
by a want of sediment during that period. The association of carnic 
and noric fauna? in the Tropites limestone of Byans might also be ex- 
plained by the want of sediment during the tuvalic and lacic periods. 
In this case the bed of the Tropites limestone although only three feet 
in thickness, might represent equivalents of the topmost division of 
the beds with Halobia comata, of the limestone with Prodydonautilus 
Griesbachi and of the Halorites beds of the Bambanag section. The want 
of sediment would be the real cause of the enormous fecundity of this 
thin layer in ammonites with carnic and noric affinities. 
The correctness of this explanation has yet to be proved by the 
results of a detailed survey of the Upper Trias.sic rocks of Byans. 
IV. — Summary. 
The two best known areas in the Triassic belt of the Himalayas 
are Spiti and Painkhanda. The sections of Byans are known to us in 
( 327 ) 
