Report of the State Geologist. 27 



the Iowa Survey, was, for one year, engaged in the service of the 

 Palaeontology of JSTew York, in making field collections and 

 obtaining geological data. Mr. Robert P. Whitfield, now Curator 

 of Geology in the American Museum of Natural History, was 

 associated with me as preparateur, draughtsman and general 

 assistant in the work for 20 years (1856 to 18T6). After this 

 date Mr. Charles D. Walcott, now Director of the U. S. Geological 

 Survey, became my assistant for two years. In the final revision 

 and publication of the four volumes, which constitute Yolume Y, 

 I had the assistance of Mr. Charles E. Beecher, now professor in 

 Yale University, from the commencement of the Cephalopoda to 

 the completion of the Lamellibranchiata, from 1878 to 1885. 

 Mr. George B. Simpson, who has served the work for many years 

 as draughtsman, has made himself very familiar with the Bryozoa 

 and. Corals of our geological formations, and has given very 

 essential aid in the preparation and publication of Yolume YI, 

 as well as in other work connected with the Palaeontology. In 

 the capacity of my private assistant, the services of Mr. Charles 

 Schuchert, now of the U. S. National Museum, were given to the 

 forwarding of Yolume YlII, as already stated in the Preface to 

 Part I. Professor J. M. Clarke, who came into the work in 

 1886, has given essential aid in the preparation of Yolumes YII 

 and YIIIj as already related in the former volume, and also in 

 Part I of the present volume, and has remained with me to its 

 conclusion. 



From the beginning of the work it has been the ambition of 

 the author to secure accurate and artistic illustrations of the sub- 

 jects under discussion. In the earlier part of the work these 

 conditions could not be obtained, but in later years the style and 

 accuracy of the representations has left little to be desired. In 

 the preface to Part I of this volume, I made acknowledgments 

 to the draughtsmen and lithographers who have been engaged 

 upon this work. The original drawings have been continued by 

 Mr. Ebenezer Emmons and Mr. George B. Simpson, and the 

 lithography by Mr. Philip Ast, who have attained a degree of 

 perfection in their work of which it is m}^ duty as well as my 

 pleasure to speak in praise. My thanks are due to the printers, 

 Messrs. Charles Yan Benthuysen & Sons, now the veteran print- 

 ing house of the country, with an uninterrupted intercourse to 



