XVI. 



represented by an unconformity. Wherearock 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 general 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 Palaeozoic time and 

 svstem are given, with the New York and other equivalents 

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

 New York Devonic is given. 



NOTB. — Tropidoleptus carinatas is a nmch more widely distributed Hamilton 

 species than Atliyris spiriferoides. The former occurs in Middle Devonian beds 

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

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

 Of the Kio Maccurti in the Amazonian district. S. A., and in the Erere, Province of 

 I'ara. Brazil. It furthermore occurs in Devonian beds at Eake Titicaca ; on the 

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

 many of these localities it is associated with Vitalina pustulosa. In some of the 

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

 regarded as of Hodcvonian age. The wide distribution of Tropidoleptus carinatus 

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

 'devonian period desirable i the Marcellus to be included in this epoch I, were it 

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

 \ arions localities. 



