INTRODUCTION TO VOL. Ill, PART I. 



HISTORICAL SKETCH OF INVESTIGA- 

 TION OF THE LOWER SILURIAN 

 IN THE UPPER MISSISSIPPI 

 VALLEY. 



BY N. H. WINCHELL AND E. O. ULRICH. 



The paleontology of the Lower Silurian, as exemplified in the rocks of Minnesota and 

 adjoining states, has been strangely overlooked and neglected. As a geological horizon 

 the rocks of the Lower Silurian everywhere bear important relations to those which 

 followed and to those which preceded them. The profuse fauna with which they are 

 characterized is the first, after the Taconic, which displays its zoological affinities with 

 distinctness, and at the same time with a sufficient number of well-preserved specimens 

 to indicate the nature of the life which filled those Paleozoic seas. As a descendant from 

 the Primordial fauna it manifests so great variations, and so great a number of species, 

 that it holds an independent rank in the paleontological record equal in importance to 

 any which followed, and superior to any that preceded. As the second great faunal epoch 

 the Lower Silurian gives the first affirmative stamp to the ide& of the evolution of species. 

 The variation of forms which began in Primordial time, once established by a careful 

 study of the "second fauna," the elucidation of all succeeding faunas by the application 

 of the same research guided by the same laws, would follow as a necessary logical result. 

 Too often this natural sequence has not been followed by paleontologists, but higher 

 stages of variation, separated perhaps by many steps from the original forms, have been 

 chosen for study and illustration. This has resulted sometimes in wrong conceptions 

 concerning the sequence of change, or the manner of development from the comprehensive 

 forms to those that are more specialized. To some species have been assigned what have 

 proved to be unnatural progenitors, and imaginary progenitors have been assumed for 

 others, while many apparently had no former ancestral species to which they could be 

 traced. The examination of the intermediate links has shown where these errors have 

 been committed. Such has been the function of the Lower Silurian fauna, as illustrated 

 in numerous instances in the preparation of this volume, 



