Williams.] INTRODUCTION. 9 
referred to for the names of those to whom I am chiefly so indebted. 
Works not mentioned in that list, such as standard reports on the 
paleontology of groups and State and Government reports on the 
geology and paleontology have also been consulted for such facts as 
bear upon the questions discussed. I wish also to acknowledge my 
indebtedness, on the theoretical side of the subject, to the suggestions 
of others, though the influence of these may not always be directly 
traceable. Barrande's theory of colonies ; Newberry's theory of cycles 
of sedimentation ; the principle of separate facies for each formation 
elaborated by Renevier; Chamberlin's theories regarding the relation- 
ship of restriction of faunal occupation of sea-bottom to continental 
oscillation and the base-leveling of continents — these have all been 
taken in and digested in elaborating the hypotheses here advanced. 
Finally, with high appreciation of valuable assistance rendered, I 
wish to acknowledge my special indebtedness to Messrs. Prosser, 
Harris, Van Ingen, Weller, Kindle, and Cleland, who, as graduate 
students at Cornell and Yale, have entered with enthusiasm into the 
investigations, and who are still engaged in prosecuting them with 
vigor and success in different parts of the field. 
