BUFFALO SOCIETY OF NATURAL SCIENCES 1 47 



rhynchus sp.,Laceripora cribrosa, but no eurypterids. In the quarry 

 at Ladjal itself, in a band of limestone apparently in place, there 

 occurred a great mass of Leper ditia baltica, and also Spirigerina 

 didyma, while in marly interbedded layers Eurypterus fischeri occurred 

 in traces. To the southeast this limestone merges into solid gray 

 limestones carrying trilobites, crinoids, brachiopods, etc., but not 

 eurypterids. At Nessoma, southeast of Sandel occurs an outcrop of 

 the upper crystalline limestones which marks the Spirigerina prunum 

 horizon, and in intercalated brown marly layers were found great 

 numbers of fish scales and breast plates, similar to those occurring 

 at Ohhessare-Pank on the southwestern end of the island. The sec- 

 tion, at Lode about the same distance west of Arensburg as Nessoma 

 is east of it, has brought to light one of the richest collecting grounds 

 on the island for the typical marine forms. Here the rock is a gray 

 limestone in which Spirigerina prunum occurs in great numbers but 

 is not well preserved; Leper ditia baltica is occasionally found, but the 

 abundant forms are: Calymene blumenbachii, Orthoceras bullatum, 

 Spirifer elevatus ,Orthis orbicularis and Chonetes striatella, all character- 

 istic of the Upper Ludlow of England (Schmidt, 241, 176-7). 



In summary, it may be said that the detailed sections bring out 

 the sporadic occurrence 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. As the beds are traced 

 to the south, southwest and southeast they are seen to be replaced 

 by those containing a pure and abundant marine fauna, but not a 

 trace of a eurypterid. Moreover, it is apparent that the occurrences 

 are in all cases immediately associated with the physical and faunal 

 evidences of a break in the series between beds of Lower and Upper 

 Ludlow age, and that this is essentially the horizon at which the 

 eurypterids ard Palceophonus nuncius are found on the island of 

 Gotland, marking in both cases what seem to be widespread river 

 deposits which precede the renewed encroachment of the sea in 

 Upper Ludlow time. 12 



12 It does not appear to me necessary to take up in detail the discussion of the occurrence of the 

 Pterygotus marl of Gotland, since the conditions there are identical with those of Oesel. The marl 

 overlies beds with a Wenlock fauna, and is succeeded by beds with an Upper Ludlow fauna. The 

 ohysical evidence of the break between the two series is marked throughout the island. This is 

 fully discussed in a forthcoming paper by Professor Grabau. 



