INVERTEBRATE ANIMALS IN" PALEOZOIC ROCKS. 



609 



§ Y. Trunk-like Concretions in the Potsdam Sandstone. 

 (Fig. 13.) 



Many years ago specimens were obtained from the Potsdam 

 Sandstone of Ontario, by the late Sir William Logan, which presented 

 the aspect of large cylindrical trunks, a foot or more in diameter. 

 They were casts in sandstone, without any external bark or or- 

 ganic matter, though showing obscure concentric lines on the ends. 

 No opinion was, I believe, hazarded at that time respecting their 

 origin; and more recently fine specimens have been collected by Dr. 

 Selwyn on the bank of the Eideau Canal near Kingston ; and Mr. 

 A. Young, a student of McGill University, obtained others at 

 Almonte, which he presented to the Peter-Eedpath Museum. One 

 of these is represented in fig. 13. 



Fig. 13. — TrunTc-lihe Concretion. Potsdam Sandstone ; Almonte, 



Canada. 



1 nat. size. 



(From a Photograph.) 



An incidental light seems to have been thrown upon their nature 

 by the study of certain recent concretions, now forming in the 

 alluvial clay of the St. Lawrence, by E-ev. Prof. Kavanagh, of 

 Montreal. These are small cyhndrical bodies with a minute per- 



