276 Alfred Sherwood Romer 



suggests, brought to the area of deposition by currents. As far as I am aware, there 

 are no published data showing the exact stratigraphic relation of the fish scales to the 

 marine fossils contained in the same zone. 



7. The Beyrichienkalk erratics 



Among the numerous glacial erratics of the north German plain, a large percentage 

 are derived from an upper Silurian formation termed the Beyrichienkalk which 

 presumably was once widely developed in the west Baltic region but is now known 

 only from erratics and deep borings (Krause, 1877; Roemer, 1885, etc.). A per- 

 centage of the erratics have yielded scales and other fragmentary fish remains, best 

 described by Gross (1947). From the nature of the case, the general stratigraphic 

 situation cannot be determined, but the age is certainly quite late Silurian, and a 

 general equivalence to the transitional Oved-Rarasasa beds is indicated. This is 

 further suggested by such ecological data as can be derived from the erratics them- 

 selves. In some cases, as the conglomeratic boulder described by Brotzen (1933 b), 

 there may be no fossils other than the scales themselves; in other instances the scales 

 are interbedded with invertebrate fossils. The remains are always fragmentary and the 

 situation suggests, as in Scania, transport from a more continental type of habitat 

 into an estuarine or near-shore deposit. 



8. Oesel 



Most famous, most interesting, and most controversial of all Silurian vertebrate 

 deposits are those of the Baltic island of Oesel, Esthonia, famous since the days of 

 EiCHWALD, Pander, Schrenk and Fr. Schmidt. The stratigraphy has been reviewed 

 by HOPPE (1931). The lower to middle Silurian beds of Esthonia — the G, H and I 

 stages — are purely marine in nature and, as would be expected, have yielded not the 

 slightest trace of a vertebrate. The uppermost beds are those of the K stage of Oesel. 

 The fauna is particularly interesting from an evolutionary point of view as the only 

 notable vertebrate assemblage in the world which is clearly pre-Downtonian in age. 

 Considered as a whole, K has an abundant invertebrate fauna, and hence Gross 

 classes the numerous Oesel vertebrates as marine. As is generally the case, however, 

 closer examination casts strong doubt on the truly marine nature of the vertebrate 

 occurrences. 



K is divided into four zones. Ki, the Rootzikiill-Karmel Zone, is a dolomitic 

 formation which varies considerably in facies both vertically and horizontally. At 

 several horizons in the western end of the island, notably at Rootzikiill and Wita, 

 there are layers which carry an abundance of the familiar assemblage of eurypterids, 

 Ceratiocaris, and a variety of ostracoderms — mainly cephalaspids with Tremataspis 

 as the most common form. In the Kj zone as a whole only nine species of presumably 

 marine invertebrates are recorded. Hoppe (43) notes that in the Eurypterus deposits 

 proper the only definitely marine forms recorded are an Orthoceras and very rare 

 specimens of Favosites and Conchidium; whether these are exactly in the fish- 

 eurypterid layers or merely stratigraphically close to them is not stated by him. 

 O'CoNNELL (1916, 143-147), after reviewing the earlier literature on this point says: 

 " In summary, it may be said that the detailed sections bring out the sporadic occur- 

 rence of the eurypterids in very thin beds, rarely intimately associated with the typical 

 marine forms which occur in beds above and below the eurypterid marls." 



