FUCOIDS OR COPROLITES. 



The middle part of the Devonian section seen along the 

 Mississippi River between Hampton in Illinois and Muscatine 

 in Iowa consists of a shaly limestone, which is quite rich in fos- 

 sils. 1 From this horizon I have for some time collected certain 

 structures, which have a close resemblance to the fossils described 

 by James Hall under the name Spirophyton, 2 and which occur in 

 the rocks of the Hamilton period in New York. The fossils found 

 here consist of flat cakes of calcareous material, from one to six 

 millimeters in thickness and from five to thirty centimeters in 

 width, intercalated among the layers of the rock, mostly lying 

 parallel with these, and presenting an endless variety of forms 

 (Figs. 1-8). The flat surfaces are bent in a succession of wave- 

 like, crescentic, low and wide ridges, which become confluent 

 and indistinct near the margin. Generally the widest ridges 

 have a corresponding depression on the opposite side of the 

 cake. 



Much of Hall's description of SpiropJiyton is perfectly appli- 

 cable to these fossils. Their substance is often "scarcely separ- 

 able from the stony matrix," especially when the containing 

 rock is unweathered. The wave-like ridges are "frequently not 

 distinctly limited on the outer margin," which then appears to 

 be continuous with a lamina in the rock (Fig. 8) . In one instance 

 there is a shallow groove following the edge of the cake on 

 either side (Fig. i) and resembling that seen in Hall's figure of 

 Spirophyton typiim? The substance of the cake contains frag- 

 ments of "small shells or fragments of shells." One of these is 



1 The part of the section to which is here referred is No. 4 in my paper, A Brief 

 Description of the Section of Devonian Rocks, etc., published in the Journal of the 

 Cin. Soc. of Nat. Hist., Vol. XIX, No. 3, pp. 93-95. 



2 Observations upon some Spiral-Growing Fucoidal Remains, etc., 16th Report on 

 the State Cabinet of Nat. Hist, James Hall, 1861-2, 76-83. 



3 Hall, loc. cit., PI. II, Fig. 2. 



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