228 CONFERENCE ON PALEOZOIC PALEOGEOGRAPHY 



suggest at once that the waters of the period were highly saline and per- 

 haps shallow; but, so far as I am aware, there is no inherent character- 

 istic of the fossil Enrypterus which can in any way suggest that it may 

 not have been a truly marine organism, and our conclusion that it was 

 not such an organism is drawn from the physical surroundings of the 

 fossil itself, rather than that the physical conditions are what we believe 

 them to be on account of some peculiarity of the fossil. 



I believe, however, that the dolomitic formations which it was intended 

 that I should discuss are the far more widespread formations of Paleozoic 

 time, such as the Magaran and Galena formations of the Upper Missis- 

 sippi Valley, and it is altogether permissible to assume that these forma- 

 tions were deposited under very different conditions than were the Water- 

 lime beds of the Cayugan. In most dolomitic formations, such as those 

 just mentioned, the fossils present are' preserved in a very imperfect con- 

 dition, almost always in the form of casts and moulds, and are often more 

 or less obliterated, so that accurate specific identifications are frequently 

 or commonly difficult or impossible, and this unsatisfactory condition of 

 the fossils themselves must be kept in mind in connection with the com- 

 parisons of faunas to be made later. In nearly all cases the fossils of 

 the calcareous beds are better preserved, more numerous, and more readily 

 identifiable than those in the dolomites. 



A comparison of fossil faunas preserved in dolomitic formations with 

 faunas of similar age in calcareous beds ought to show whether the life 

 of these ancient seas was notably reacted upon by the conditions which 

 have been responsible for the existence of our conspicuous dolomitic 

 formations. A comparison of this sort has been attempted between the 

 fauna of the dolomitic Galena formation of Illinois, Wisconsin, Iowa, 

 and Minnesota and the fauna of the typical Trenton limestone of the 

 east, two formations which are believed to be essentially contemporaneous. 

 A census of the Galena fauna, in which it has been the purpose to ex- 

 clude all forms except those which occur in the dolomitic facies of the 

 formation, has been compiled. Perhaps the most characteristic member 

 of the fauna is Eeceptaculites, several species of which genus are recorded, 

 of which R. oweni is the most common. This genus is represented in the 

 typical calcareous Trenton limestone of New Jersey and elsewhere in the 

 East, and the most characteristic Galena species occurs in such great 

 numbers in the upper portion of the calcareous Kimmswick limestone 

 of southeastern Missouri that this formation was called the Receptaculite 

 limestone by the early Missouri geologists. The corals are sparsely rep- 

 resented in the fauna, an undetermined species of Streptelasma being the 



