vi PREFACE. 



ihe authors wish to thank all who, in one way or in another, by 

 furnishing material, suggestions, illustrations, etc., or by criticism 

 have furthered this work. They can not forbear to mention their 

 special indebtedness to Professor John M. Clarke, who has gener- 

 ously loaned illustrations and in other ways has been helpful; to 

 Mr. E. O. Ulrich and Dr. R. S. Bassler; to Professors Cumings, 

 Sardeson and Stuart Weller ; to Dr. C. P. . Berkey and to Dr. 

 Percy E. Raymond, who has furnished a number of illustra- 

 tions and some descriptions, as well as lists of species. Spe- 

 cial acknowledgments are further gladly made to Florence Henry 

 Shimer, A.M., and to former and present students of the 

 senior author, especially Elvira Wood, A.M., and Fred. K. Mor- 

 ris, A.B. The generous manner in which American state geolo- 

 gists and boards of surveys have illustrated their palseonto- 

 logical publications has made possible the full illustration of this 

 work; constant and free use has been made of all such publica- 

 tions with the full confidence that their authors and editors sanc- 

 tioned such usage. In all cases (except where omitted by 

 oversight) the source of the illustrations has been given. The 

 descriptive material has been largely adapted from the original 

 descriptions and figures, published in the volumes of the various 

 surveys, societies, universities, etc., aided and checked, as far as 

 possible, by examination of material from type localities. 



The earlier chapters through the brachiopods appeared during 

 the years 1906 and 1907, being published serially in the Columbia 

 University School of Mines Quarterly. The remainder of the 

 work now makes its first appearance. The authors trust that it 

 may serve the needs of American students of palaeontology and 

 stratigraphy, to whom it is cordially dedicated. 



New York and Boston, 

 October 1, 1909. 



