No. 4. — Expedition to the Baltic Provinces of Russia and Scandinavia, 



1914. 



P.\RT 2. — The Silurian and High Ordovician Strata of Esthokia, 

 Russia, and their Faunas. 



By W. H. Twexhofel. 



TABLE OF CONTENTS. 



Part 2. 



Page. 



Introduction 289 



The Russian Section 291 



The Ordovician System . .- 293 



The Silurian System 314 



Part 3. 



Introduction 341 



Conclusions 354 



Explanation of Plates 



INTRODUCTION. 



The present paper is based on work done under the auspices of the 

 Shaler Memorial fund. In company wnth Prof. Percy E. Raymond, 

 an expedition was undertaken in the summer of 1914 for the purpose 

 of examining the Cambrian, Ordovician, and Silurian .strata exposed 

 around the Baltic in Russia, Sweden, and Nonv^ay, with the object 

 in view of attempting a correlation with strata of the same systems 

 of eastern North America. The wTiter was primarily concerned with 

 the highest Ordovician and Silurian, while the Cambrian and the 

 remainder of the Ordovician were studied by Professor Raymond, 

 although mutual assistance was rendered. The outbreak of the war 

 to some extent necessitated a curtailment of the study, but in my case 

 this amounted to the loss of only a few days' work in northern Got- 

 land and a considerable shortening of the time allotted to Norway. 

 The failure to see certain sections of northern Gotland will be ulti- 

 mately overcome by detailed collections which have been made (1915) 



