76, 
HAMILTON GROUP. 
193 
Nodules of iron pyrites, often embracing a fossil in the centre, are 
of frequent occurrence; they are usually uninteresting, except as 
showing the incipient stages of this process. The small figure in the 
margin represents one of these aggregated around a Loxonema, a 
portion of which projects above. 
The septaria are spherical, flattened or oblong, and crossed by numerous seams of calcare¬ 
ous spar, and in the centre is frequently a cavity lined with crystals and partially filled with 
fluid bitumen. The figure below represents a small specimen of this kind from the shore of 
Lake Erie. It is figured for the purpose of illustrating the general appearance of these bodies, 
which are frequently taken for some fossil.* The calcareous concretion is first formed, and 
afterwards cracks, and the spaces become filled with crystalline matter from segregation or 
infiltration. Sometimes there are no cracks in them, and at others these are filled with clay 
or shale. 
Localities — The description of this group has necessarily led to the mention of many loca¬ 
lities ; but as the object of this head is to direct observers to the most important points, I may 
mention the banks of Cayuga and Seneca lakes, the ravines on the Genesee river, in Avon, 
* The common belief is that these bodies are petrified tortoises or turtles, and that the seams are the divisions of the 
plates of the shell. So firm is this belief with many persons that they are kept as an evidence of former living animals, 
while the multitudes of shells in the saute rock are entirely overlooked. 
[Geol. 4th Dist.J 
25 
