218 Peculiar Fossils from the Chemung Rocks. 



stalt, I, 3, p. 3). These views have not been generally accepted, 

 however, and no satisfactory conclusion has been reached in re- 

 gard to the botanical relations of Spirangium. 



The first impression of the writer in examining the fossils now 

 under consideration, was that they were the stems of algae. 

 They are mere casts, all traces of the original structure having 

 disappeared, as is generally the case with fossilized sea-weeds. 

 It is also true that in the same and adjacent formations the re- 

 mains of fucoids w r ith spiral fronds, Spiropliyton, are not un- 

 common. The stems of Spiropliyton, however, are never found 

 stripped of the fronds, and nothing which resembles the fossils 

 before us has been detected in a careful examination of the upper 

 extremity of the stems of Spiropliyton The Archimedes Screw, 

 Retepora Archimedes, has a great lesemblance in form to these 

 fossils, but that is a calcareous animal organism, of which the 

 structure is very easily made out, for the salient revolving ridges 

 which it bears are only the bases from which the expanded fronds 

 of a Bryozoon have been torn away. On the contrary, Spiraxis 

 is a simple cast, no calcareous matter remaining, as would cer- 

 tainly be the case if it represented a coral or mollusk. The 

 original substance has entirely disappeared, and yet it had suffi- 

 cient solidity to form a defined mould in the sand where it was 

 buried ; and when the organic tissue disappeared, as it did com- 

 pletely, the cavity was filled by infiltration, and a perfect cast 

 was thus produced. Nothing is more common than to find the 

 casts of sea-weeds formed in this way ; but it is also true that 

 sponges are sometimes fossilized in a similar manner. The 

 group of Dictyospongia, formerly considered sea-weeds, and de- 

 scribed under the name of Dictyophyton, generally exhibit the 

 same absence of organic structure, and are simply casts in the 

 sandstone ; but they have been referred to of late by all writers as 

 sponges, and in some instances slight traces of original tissue have 

 been preserved, which place their true character beyond a doubt. 

 Among the sponges there are none known to the writer which 

 exhibit anything like the regular spiral structure which is char- 

 acteristic of our fossils ; but a tendency to a spiral mode of growth 

 appears in some sponges, and is very distinctly seen in Hyalo- 

 nema, and in Siphonoccelia, Roemer, (Stachyspongia, Zittell). 

 No positive evidence can therefore yet be adduced to satisfy the 



