RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 329 



The facts which constitute the evidence as to the variety and char- 

 acter of the no nmarine formations, and that of their distinction from 

 those of marine origin, are usually well understood by those geologists 



who are also naturalists because the subject to which they relate is 

 mainly biological, but they are often not so well understood by the 

 general reader, nor by those who pursue their geological studies wholly 

 upon physical grounds. For these reasons the following statements 

 and dismissions, while they are in some respects necessarily technical, 

 are, so far as practicable, expressed in an elementary manner. 



The evidence that the greater part of the sedimentary rocks of the 

 earth, those which constitute the formations containing the records of 

 its past biological history, are of marine origin is based almost wholly 

 upon the character of their contained fossil remains, and is, as has just 

 been intimated, so abundant and complete that it can not be seriously 

 questioned. That is, it is evident that they were deposited either in 

 oceanic waters or in those of similar saltness whose geographical extent 

 were more restricted by land areas, such, for example, as the present 

 oceans on the one hand, and the Mediterranean and Red seas on the 

 other. All these are designated as marine deposits, and the waters in 

 which they were formed are understood to have rested at that world- 

 wide level which is usually termed sea level, but which is herein written 

 ocean level, because in this essay the term sea is used in a somewhat 

 restricted sense. 



The other sedimentary rocks were deposited in other than oceanic 

 waters. Most of them so much resemble marine formations in litho 

 logical and stratigraphical character, that it is only by means of the 

 peculiar character of their fossil remains that it is known that their 

 deposition took place either in fresh waters or in those which contained 

 salt in less proportion than it is contained in oceanic waters. All these 

 are designated as nonmarine deposits. They usually occupy smaller 

 districts than do marine deposits but a few of them rival the latter in 

 thickness and geographical extent. 



Nonmarine deposits are more varied in both character and origin 

 than is indicated by the mere evidence which they may afford that salt 

 was present in, or absent from, the waters in which they were accumu- 

 lated, because the physical conditions were in each class of cases con- 

 siderably different, ruder the head of nonmarine sedimentary depos- 

 its are placed those which, from the inherent evidence they respectively 

 afford, are assumed to have been formed in liuviatile, estuarine or lacus- 

 trine waters, or in the waters of lagoons, bays, or inland seas. The 

 first three terms just mentioned are of themselves sufficient to indicate 

 that the deposits to which they are applied were laid down in formerly 

 existing rivers, estuaries or lakes. There are certain other nonmarine 

 deposits with which the geologist sometimes comes in contact, namely, 

 those of littoral and of palustral origin. The former are produced 

 along the shores of broad bodies of water and the latter in the swamps 

 and shoals which frequently border the same. 



