CARBONIFEROUS FRESH-WATER LIFE. 87 



call for special mention, and each is worthy of still further investigation: 

 First, the occurrence near the base of the limestone of a fresh- water fauna; 

 second, the varied development of the Lamettibranchiates, a class which has 

 heretofore been but sparingly represented in the collection of Carboniferous 

 fossils from the Cordillera ; third, the mingling near the base of the horizon 

 of Devonian, Lower Carboniferous and Coal-measure species in gray lime- 

 stone directly overlying beds characterized by a purely Coal-measure fauna. 



Fresh-water Life. The lowest strata from which we have any record of 

 organic life from this epoch are found at the extreme northeast corner of New 

 York Mountain, and also near the railway cut immediately south of the 

 Richmond furnaces. Both localities lie just east of the Hoosac fault, which 

 brings up Carboniferous beds against the Silurian. But for the alluvial 

 deposits, which occupy the valley, the beds of the two localities would 

 probably be found to be continuous; the rocks in botli are similar. There 

 occur here 100 feet or more of fine clays and grits, interstratified with 

 arenaceous and argillaceous limestones passing up into pure limestone, 

 showing abrupt changes and rapid deposition. In these transition beds 

 were found abundant evidence of a varied fresh-water life, it being possi- 

 ble to determine several distinct species. The shells indicate a shallow 

 water fauna, as is also clearly established by the mode of deposition of the 

 sediments. Mingled with these shells are a few fragmentary bits of twigs 

 and stems of plant life, for the most part referable to a coniferous growth, 

 and showing signs of having been washed down from a land surface that 

 could not have been very far away. Mr. Walcott has briefly described 

 three species: one belonging to the genus Physa, named by him P. priscu; 

 another form is a pulmonate shell, allied to the genus Auricula, and to 

 which he has given the name Zaptychius carboiiaria; a third shell is related 

 to, if not identical with, Ampullaria, and is provisionally named after the 

 Director of the Geological Survey, A. powetti. The discovery of fresh or 

 brackish water shells so low down in the Paleozoic and so remote from any 

 known locality of similar beds renders their mode of occurrence one of 

 peculiar interest. 



Lameiubranchiate Fauna. From the horizon of the Lower Coal-measures 

 there have been collected over forty species of Lamellibranchiate shells, a 



