590 A. W. GRABAU LOWER ORDOVICIC FORMATIONS 



The fauna of the Megalaspis limbata limestone at the Kinnekulle does 

 not occupy the whole of the Lower Red Orthoceras limestone, for a part 

 of this rock, according to Moberg, falls into the Asaphus limestone. Gr. 

 Holm, however, makes the Limbata limestone the equivalent of the Lower 

 Eed Orthoceras limestone of the Kinnekulle quarrymen. Under the term 

 Asaphus limestone have been included all those beds in which species of 

 Asaphus predominate over species of Megalaspis, and it would appear 

 that the beds designated are not always exact equivalents in different 

 sections. At the Kinnekulle the fauna of ibis division differs markedly 

 from that of the Limbata limestone, though, as will be seen by a glance 

 at the list of the Asaphus limestone fauna given above, the genus Mega- 

 laspis is still present. Indeed, that genus ranges through a considered) I e 

 portion of the Orthoceras limestone, while with us the species referred to 

 it are confined to the lower western Beekmantown, with the exception of 

 one species described from the Lower Richmond of Iowa. 



THE ORTHOCERAS LIMESTONE OF ESTHONIA 



Before considering the Orthoceras limestone of northern Scandinavia, 

 it will be well to note the characteristics of the equivalent formations in 

 the Baltic provinces, Esthonia and Saint Petersburg, on the south side 

 of the Gulf of Finland, and approximately due east from the Swedish 

 locality just discussed. This section, which I have not visited myself, 

 has been described in considerable detail by Fr. Schmidt, and more 

 recently by Lamanski and by F. v. Huene (Centralbl. fiir Min., etc., 

 1904, No. 15 ). 24 



Bassler, in an elaborate memoir on the early Paleozoic Bryozoa of the 

 Baltic Province, gives a summary of the section and a list of the species 

 of fossils reported from these formations with an indication of their range 

 in the several subdivisions of the series. This list, though in some re- 

 spects faulty (see the criticism by Axel Born), nevertheless is of great 

 value, and Bassler has performed a distinct service for which students ot 

 the early Paleozoic rocks owe him gratitude. 



In this region the section begins with the Lower Cambric Esthonia for- 

 mation (Marcou), which rests on the pre-Cambric granite or gneiss and 

 has a thickness of 100 meters or more. It includes a basal sandstone and an 

 intermediate thick layer of plastic blue and greenish clay, and is followed 

 by sandy layers with intercalated clayey layers, which carry Mesonacis 

 {Schmidtiellus) mickwitzi, Michwitzia moniliforme, and VoIlborihelJa, 



24 Since this paper has been completed, the important paper on "The correlation of the 

 Ordovician strata of the Baltic basin with those of eastern North America," by Percy B. 

 Raymond, has appeared (Bull. Mus. Comp. Zool.. vol. lvi, No. 3). Reference will be 

 made to it in the following pages in footnotes. 



