248 GENERAL GEOLOGY. 



during the deposition of the calcareous material of this 

 formation, than during the deposition of the sandy and 

 shaly material of the two which preceded it. Very many 

 of the species common in and characteristic of this forma- 

 tion, range without interruption through the whole series of 

 strata that constitute the Lower, Middle, and Upper coal- 

 measures. A few species, it is true, seem to be confined, 

 respectively, to each one of these three formations, or are 

 otherwise restricted in their vertical range so far at least as 

 Iowa is concerned. Thus Chonetes mesoloba seems to be con- 

 fined to the Middle and Lower, while Spirifer opimus has 

 not been recognized above the Lower, etc., etc. Some of the 

 species of the Upper coal-measures are confined to that 

 formation alone, but seem to appear in any part of it that 

 presents similar lithological characters, evidently indicating 

 that the material they are imbedded in, formed a congenial 

 habitat for them while living.* 



Vertebrates are, so far as ascertained, represented by the 

 remains of fishes alone, which belong to both orders, Sela- 

 chians and Ganoids; the former being most common, 

 although rather rare. The Ganoids have not yet been studied ; 

 the following Selachian genera have been recognized: 

 Cladodus, Diplodus, Petalodus, CJwmatodus, Peripristis, 

 Petrodus, Helodus, Psammodus, and Deltodus. 

 . Articulates. Two species of trilobites, belonging to the 

 genus PMUipsia are found, but they are not common. The 

 Ostracoid genera Cytlierina and Beyricliia are not unfre- 

 quently met with. Of the latter there are two species, one of 



*It was with surprise and great regret that in the latter pirt of the year 1867, I 

 received a copy of a work by Dr. H. B. Geinitz, of Dresden, Saxony, entitled, "Car- 

 bon formation and Dyas in Nebraska," and learned from it that that able palaeontolo- 

 gist had referred certain fossils described in it which were collected by Prof. Jules 

 Marcon from the rocks of Eastern Nebraska, to the Dyas (Permian) and others from 

 other localities but in the same region partly in Iowa, to the Kohlenkalk (Sub-car- 

 boniferous limestone). I have elsewhere in this report, shown in the plainest manner 

 that no Sub-carboniferous limestone can exist along the valley nor in the vicinity of 

 that part of the Missouri river which divides Iowa and Nebraska. Whether the strata 

 which do exist in Western Iowa and Eastern Nebraska are of Permian or Upper coal- 

 measure age, may, in a manner, be regarded as a mere question of terms. If any 

 Permian strata exist there, then indeed are all our Iowa strata of Permian a«e down 



