PALAEONTOLOGY OF IOWA. 475 



of the same class, and represent the forms, chiefly, of Cri- 

 noidese and Brachiopoda, which are most commonly found 

 in these limestones. No species common to the two lime- 

 stones have been observed by myself; and though probably 

 such do occur, they are certainly not numerous, nor among 

 the prominent forms which every where mark the two 

 rocks. 



Besides the collections which I have been able to procure, 

 I have availed myself in many instances of those already 

 made. Mr. A. H. WORTHEN very kindly offered me the use of 

 his extensive and magnificent collection of Crinoidese, as 

 well as of -other fossils ; and but for this liberality, the work 

 would have been far less fully illustrated. Such collections 

 can only be accumulated by the devoted attention of many 

 years ; and in expressing my own indebtedness to Mr. WOR- 

 THEN, I may express the obligations under which geology 

 rests for this contribution, and which will be gladly acknow- 

 ledged by every student and votary of the science. 



The collections made by Mr. WHITNEY and Mr. HUNGERFORD 

 from the Hamilton group on Lime creek near Rockford, pos- 

 sess peculiar interest ; inasmuch as they present us with 

 forms more nearly allied to those of Central Europe, than 

 the species w T hich occur in more eastern localities of the 

 same formation. The collections made by these gentlemen, 

 and by Mr. WORTHEN at Independence and other centrally 

 situated localities, show that in progressing in a northwes- 

 terly direction, changes are observed which can only be 

 attributed to climatic or geographical influences. 



The explorations both in the Hamilton and Chemung 

 groups, as well as in the Carboniferous limestones, are yet 

 very incomplete towards the northern part of the State, and 

 we have reason to believe that discoveries of much interest 

 will be made in these formations in that direction. 



The surveys of the Desmoines valley in 1856 proved the 

 Gypsum formation to lie above the productive Coal measures . 



