238 LA TOUCHE : GEOLOGY OF NORTHERN SHAX STATES. 



Mr. Cowper Reed has already discussed the composition and 

 . _ . . zoogeographical elements of this fauna at page 



Affinities of fauna. -, et e , • n T • i T , 1° 



154 et sec/., of his Memoir, and I have little 

 to add to his remarks. He calls attention to the predominance 

 of European types, no less than 56 species from the Calceola stage 

 of Western Europe being represented out of a total of 166, while 

 62 other species are either identical with, or closely allied to, species 

 occurring in the Devonian of Europe at other horizons. Only twelve 

 of these are enumerated by Mr. Reed as not found below the upper 

 part of the middle Devonian or belonging to higher horizons. 

 On the other hand, the American element is represented mainly 

 by allied forms, and the resemblance is most close among the 

 Bryozoa, certain of the Padaukpin genera (e.g., Selenopora and 

 Buskofora) not having been previously detected outside the American 

 continent. 



Too much stress, however, must not be laid upon the affinities 

 Organisms preserved at or the composition of the fauna discovered at 

 Padaukpin. this single locality in discussing the distribu- 



tion of invertebrate life at this period. It should be remem- 

 bered that the Padaukpin fauna has only been found at one 

 spot, covering an area of perhaps 100 square yards, and that it 

 may throw little light upon the nature of the organisms that 

 produced the bulk of the enormous mass of limestone that 

 extends over the Shan States. I have already pointed out, as 

 Mr. Cowper Reed remarks (Op. cit., p. 154), that those organisms of which 

 the casts only have been found at Padaukpin, such as the mollusca, 



are those in which the original shell was 

 Instability of aragonite. , . , , „ , 



composed, either partly or wholly, of aragon- 



ite. Several observers 1 have shown that the absence of the 



remains of certain classes of organisms from limestones may be 



explained by the difference in stability between calcite and ara- 



gonite ; and it seems possible that the predominating forms of life 



which produced the great bulk of the Plateau Limestone were 



mollusca, and that the Padaukpin fauna, rich as it is, gives a very 



incorrect picture of the life of the period in the Burmese region. 



_ In the railway cuttings through the limestone 



Remains of mollusca. . , 0 , ,, • t 



on the zig-zags above bedaw the remains ot 



1 Gustav Rose, t)ber die hetoromoi phcn Zustiinde der kohlensaufen Kalkerde ; 

 Abhandl K. Preuss. Akad. Berlin, 1858. p. 63 : H. C. Sorby, Presidential Address, Geol. 

 Soc. Lond., 1878 : V. Cornish and P. F. Kendall, on the Mineralogieal Constitution of 

 Calcareous Organisms ; Gcol. Mag., 3)ec. 3, Vol. V, p. tit'. 



