BALTIC EEGIOX 



59' 



the underlying green marly beds which form a transition to the G-lauconite 

 sand below (B I) also belong to this horizon. The fauna is especially 

 characterized by Megalaspis planilimbata Aug. in the lower and 1[. lim- 

 bata Sars. and Boeck, M. pohjpliemus Brogg., and Asaplms priscus Larnsk. 

 in the upper part. Ptyehopyge, Xiobe, Ampyx. Ilhenus, and Cyrto- 

 metopis are also represented. Besides this there are a number of species 

 of Orthis, many of them identical with or close mutations of the species 

 found in the underlying B I /? beds. 



The second division. B II /3, known locally as •'"'Sheltjaki/* consists of 

 thin-bedded, less compact, mottled limestone with sporadic glauconite 

 grains. Its thickness is 1.S0 meters. It is especially characterized by 

 Asaplms broggeri Dalni. and Onclwmetopus volborthi F. S., and contains, 

 besides two species of Megalaspis [1[. l-olenl-'i F. S. and M. lujorrliina 



.SCOTLAND 



ENGLAND 



SCAHDMAVIA 



SIBERIA 



Figcee 4. — Ideal Section illustrating the Relationships of the several Types of Deposits 

 in the north Scottish. Atlantic, and Siberian Provinces in Lower Ordovicic Time 



In the north Scottish region the Durness limestone facies (Ds.) with Beekmantown 

 fossils occurs. In the central or English region i.Atlantic provincel graptolite shales 

 predominate, the Dictyonema shales (D) being succeeded by the Phyllograptus shales 

 (Ph.). In the eastern or Siberian region limestones predominate, with the Ceratopyge 

 and earlier beds below (C), followed by the Megalaspis limestone (IT). 



F. S.)j Niobe lindstromi F. S., Xileus armadillo var. depressa Sars. and 

 Boeck. two species each of Cyrtometopus and of Illsenus, and one each of 

 Pterygornetopus and Amphion. The generic relation of this trilobito 

 fauna to that of the Ceratopyge horizon is evident, though the species are 

 mostly distinct. Of the species of Orthis and Orthisina, some continue 

 from the underlying beds, while all but one of the species of Porambonites 

 found in B II (3 also occur in B II a, and all extend up into B II y, but 

 not above this horizon. 



The third division, B II y, consists of rather compact gray limestone. 

 known locally as "Friese," and having a thickness of 2.40 to 2.70 meters. 

 It is separated from the overlying B III a by a wavy surface above which 

 glauconite abounds. This horizon contains a rich fauna in which Asaph us 

 lepidurus and Megalaspis gibba are considered the leading types. Three 

 other species of Megalaspis are found here, one of them continued from 

 the bed beneath, as is also Onclwiaetopus volborthi F. S., Ptyehopyge 



