represented bv an unconformity. Where a rock series is locally 

 divisible into more or fewer than three groups, one of these 

 local groups may correspond to a portion of a group in the 

 general division, or to more than one of those groups. It 

 remains for the student of the local group to adjust them to 

 the oreneral scheme, which is to serve as a basis for cor- 

 relation and comparison. 



The rock svstems include those rocks which were formed 

 during the corresponding great time division. Both series 

 and system take the names of the corresponding eras and 

 times . 



In Table A, the subdivisions of the Paleeozoic time and 

 system are given, with the New York and other equivalents 

 in common use. In Table B, the detailed subdivision of the 

 New York Devonic is g-iven. 



Note. — Tropidoleptus carinatus is a mucb more widely distributed Hamilton 

 species than Atbyris spiriferoides. The former occurs in ^Middle Devonian beds 

 throughout New York, at the Falls of the Ohio, and at various localities in Ohio, 

 Pennsylvania and Illinois. It is also abundant in the Middle Devonian sandstones 

 of the Rio Maecuru in the Amazonian district, S. .\., and in the Erere, Province of 

 Para. Brazil. It furthermore occurs in Devonian beds at Lake Titicaca ; on the 

 Rio Sicasica, Bolivia; in South Africa; in France, Germany and England. In 

 many of these localities it is associated with Vitulina pustiilosa. In some of the 

 last mentioned localities however, the beds characterized by these species are 

 regarded as of Eodevonian age. The \vide distribution oi Tropidoleptus carinatus 

 would make the adoption of the name Carinatus epoch for a single epoch of the 

 Alesodevonian period desirable (the Marcellus to be included in this epoch), were it 

 not for the discrepancy in the ages of the beds characterized by this species at the 

 various localities. 



