So as the results of observation and of study accumu- 

 lated, it became evident that two related but distinct vol- 

 umes were needed, in order that the conclusions reached 

 might be placed properly before the scientific world. That 

 now presented was written in 1920-21, and finished in Au- 

 gust of the latter year. The other, which bears title : 

 "Fishes the Source of Petroleum," was largely written from 

 the early part of 192 1 onward, and was finished in Decem- 

 ber of 1922. Any discriminating reader of the two volumes 

 will readily perceive that some such history attaches to them. 



In preparing both volumes the writer has endeavored 

 to quote the exact words of authors whose observations 

 he has referred to. The reader therefore can now share 

 with the writer the pleasure of examining original, and so 

 ever-fresh, statements that bear on questions at issue. 



While the writer has spent years in study of rock forma- 

 tions and their included organic remains, it is of necessity 

 true that many of his statements have been derived from 

 examination of the published investigations of others. Such 

 also is true of the abundant zoological results here pre- 

 sented. But for any defects that may be shown in this 

 presentation, the writer desires to be alone responsible. If 

 therefore conclusions are here reached that will advance 

 scientific truth, such deserve to be conserved; should some 

 prove to be incorrect, they can readily be discarded. For 

 all scientific 'advance has shown that Truth alone will en- 

 dure, error and misstatement will fade away. 



Special and grateful acknowledgment is now made of 

 the invaluable aid furnished by the writings, and in some 

 cases by the illustrations, of A. S. Woodward; of his early 

 teachers and friendly helpers Sir A. Geikie and Dr. R. H. 

 Traquair; of his university predecessor or colleague, Pro- 

 fessors Leidy and Cope. In dedication of this volume to 

 a lady who has ever striven to aid and advance scientific 

 progress, the author pays a small but deserved tribute. 

 The printers and publishers of it have shown that considera- 

 tion and regard, which ensure that it can worthily see the 

 light. 



Philadelphia, April, 1923. 



