GEOLOGICAL IMPORTANCE OF SEDIMENTATION 323 



the several kinds of deposits may be distinguished according to their 

 mode of origin ; and, lastly, to apply the foregoing principles to a few 

 examples, in order to illustrate their use, and to interpret the geog- 

 raphy and climate of preceding ages. 



In order to bring together the facts for such a discussion, it is only 

 necessary to search the abundant literature of the past fifty years ; but 

 the writer has found no single article which presents the subject in 

 quite this way, or arrives by this method at the conclusions to which 

 he has come in regard to the relative importance of certain classes of 

 deposits and their distinctive features. It has seemed worth while, 

 therefore, to arrange portions of this in form for publication, omitting 

 much which is necessary for class work, but which can be found ably 

 developed in various books and articles, and enlarging on other por- 

 tions which are not so fully discussed elsewhere. 



For this presentation it seems best to give, first, an inductive dis- 

 cussion of the relative importance of continental, littoral, and marine 

 deposits, as observed under process of present or recent formation, 

 and to follow this by an abstract and deductive discussion as to the 

 chances for the preserval in general of these several classes of deposits ; 

 and, finally, to close with another deductive argument as to the vary- 

 ing relative importance through geological time. This latter discus- 

 sion should, however, be kept free from positive statements of opinion 

 upon individual formations, in regard to which there may be doubt or 

 difference of opinion; the purpose of the article being accomplished 

 in merely opening the question as to what kinds of deposits should be 

 expected to predominate, from the premises of our present ideas in 

 regard to the geography and climate of past geological times. It 

 would be suitable for a later article, however, to discuss in detail cer- 

 tain distinctive chemical, textural, and structural features charac- 

 teristic of the several kinds of deposits, and to apply these to individual 

 formations, thus confirming or disproving by an inductive process 

 the preceding general conclusions arrived at by deductive reasoning. 

 Only by a combination and confirmation of these two methods can 

 safe conclusions be arrived at in interpreting the fragmentary remains 

 of the results of unseen and now vanished processes. 



Either inductive or deductive methods used by themselves are 

 always liable to error, since we can seldom be sure that man has appre- 



