In Silurian and Devonian Epochs 105 



pears to show that the green and grey mudstones were 

 laid down in close proximity to a land area, and at the 

 most can imply only estuarine conditions." 



Campbell further draws attention to the striking simi- 

 larity of beds described by Kiaer {61) for the Christiania 

 region, since the contained organisms seem at least generi- 

 cally identical, and include several types of fish. 



Kiaer entitles his paper "A new Downtonian Fauna in 

 the Sandstone Series of the Kristiania area." This series 

 is fully 500 meters thick, and consists of a lower part rich 

 in shales, and an upper part poor in shales. Fossils and 

 clear trail marks only occur in the lower part, while the 

 richest horizon is a "gray-green calcareous and argillac- 

 eous sandstone, which can be easily split into somewhat thin 

 and irregular slabs." He describes the subjoined group 

 of wholly freshwater organisms : 



(i) Dictyocaris, very common. 



(2) Ceratiocaris, not often in good specimens. 



(3) Eurypterus norvegicns, very common. 



(4) Eurypterus minutus, rare. 



(5) Eurypterus sp. rare. 



(6) Pterygotus sp. rare, in fragments- 



(7) Aceraspis robustus, very common. 



(8) Micraspis gracilis, not common. 



(9) Pterolepis nitidus, very common. 



(10) Pharyngolepis oblongus, not common. 



(11) Rhyncholepis par'viilus, common. 



The five last were all new anaspid or hyperplacodous 

 fishes (p. 257) that show near aflinity with Scottish and 

 later evolved Canadian types. He regards the entire series 

 "of Phyllocarids, Eurypterids, and Ostracoderm fishes" as 

 freshwater, but records a set of marine types in what he 

 calls an "uppermost marine Ludlow zone." An almost 

 identical association of organisms also was recorded by J. 

 V. Rohon {16) in rocks of the island of Oesel in the Baltic. 



During the past 30 years an examination of the Upper 

 Silurian rocks of the Eastern States and Canada has re- 

 vealed a surprising similarity — almost close identity — with 

 those of the Old World. Thus the lower strata of the 

 former region that have been called the Niagara and 

 Guelph seem to represent the Aymestry and related marine 

 strata of England. The succeeding and higher beds again, 



