NEW TR1LOBITES FROM THE MAQUOKETA BEDS OF 

 FAYETTE COUNTY, IOWA 



BY ARTHUR WARE SLOCOM 



The specimens upon which this paper is based represent the results 

 of two visits to Fayette County, Iowa, made by the writer, one in July, 

 1 910, and the other in October, 191 2, supplemented by specimens from 

 the collection of Mr. A. G. Becker of Clermont, Iowa, and from the 

 collections of the State University of Iowa. 



The Maquoketa beds constitute the uppermost deposits of the 

 Ordovician system found in the state of Iowa. In a few localities they 

 are overlaid, unconformably, by Niagaran limestones, but usually they 

 underlie the drift. These beds have been worked out by Savage in his 

 "Geology of Fayette County."* He divides the formation into Lower, 

 Middle and Upper Maquoketa beds. The Lower member attains a 

 maximum thickness of 95 feet and consists of alternating layers of 

 shale and argillaceous limestone. Some of the layers are quite fos- 

 siliferous. The Middle division consists of 40 to 60 feet of cherty 

 limestone with few fossils. No trilobites have been observed from 

 these beds. The Upper division has a thickness in some places of 

 125 feet. It is composed of a plastic blue-gray shale. In the upper 

 portion occurs a zone 8 to 12 feet in thickness, in which are thin cal- 

 careous layers composed almost entirely of fossil shells. Below this 

 zone the shale is practically barren of fossils, but contains numerous 

 crystals of selenite. The lithological characters of the various divisions 

 of the Maquoketa beds are quite constant at the various exposures 

 studied. 



The Maquoketa beds of Fayette County afford a fauna of unusual 

 interest both as to the number of species represented and the excel- 

 lent state of preservation of the specimens. Other localities afford a 

 greater number of individuals, but few, if any, excel it in the quality of 

 the material. Savage f reports 68 species divided as follows: Sponges 

 2, Corals 2, Brachiopods 31, Pelecypods 4, Gastropods 11, Pteropods 2, 

 Cephalopods 7, and Trilobites 9. 



In the material collected and identified by the writer, the number 

 of species obtained in the various groups agrees practically with the 

 above list with the exception of the trilobites. Of these twenty species 



*Iowa Geological Survey, 1904, Vol. XV, pp. 433-546. 

 tLoc. cit., p. 486. 



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