76 NEW YORK STATE MUSEUM 



Hill conglomerate, described by the writer from the neighborhood 

 of Albany (see page 80). 



This belt was probably first noted by Emmons who indicated 

 it on his map accompanying his Agricultural Report^ and gave 

 a section through Bald mountain in his paper on the Taconic 

 series in the same report. He identified it with the " Calciferous 

 sandstone " (Beekmantown), distinguishing a blue portion of purer 

 limestone and a lighter one. He included, however, the thin-bedded 

 limestone on top of the mountain in the " Calciferous sandrock." 

 This latter has been shown by Walcott (op. cit., page 317) to be of 

 Cambric (Georgian) age, a fault separating the Georgian rocks from 

 the limestone belt (see chapter on structure of Bald mountain, page 

 108). Walcott, who first correctly separated on a map the Or- 

 dovicic and Lower Cambric areas of the slate belt {op. cit., plate 3), 

 also indicated the extension of the limestone belt and gave a section 

 of Bald mountain in which he distinguished " Calciferous sand- 

 rock " (the lower darker rock) separated by dark shales from 

 " Chazy limestone." From a locality {op. cit., page 317) about 2 

 miles north of Bald mountain, Trenton fossils (Dalmanella 

 t e s t u d i n a r i a , Rafinesquina alternata, Mac- 

 lure a and other gastropods, Calymmene senaria and 

 fragments of Asaphus platycephalus) are cited. It is 

 thus seen that Walcott held the view that the limestone belt contains 

 Calciferous, Chazy and Trenton rocks, a view also expressed on 

 plate 3. Dale has on his map of the slate belt (1899, plate 13) dis- 

 tinguished the limestones simply as lower Siluric (Ordovicic) lime- 

 stone from the Lower Siluric shale, etc., stating (page 190) : '* The 

 Trenton limestone occurs sporadically within the Ordovician areas 

 of the slate belt ; also on its western edge in Argyle and in Hart- 

 ford. In some places it was probably deposited contemporaneously 

 with the Hudson grit and shales, or it may underlie a portion of 

 them. In others it may represent the entire Lower Silurian series 

 and should then be regarded as Trenton, Chazy and Calciferous." 



We see from this quotation that the determinations of the age of 

 the Ordovicic limestone in the slate belt are rather insecure, a fact 

 that can be readily explained by the scarcity and poor preservation 

 of the fossils usually obtained there. 



On the Geologic Map of New York, published by F. J. H. Mer- 

 rill (1901), the limestone belt on the west edge of the Georgian is 

 entered simply as Trenton. 



1 Emmons, Ebenezer. Agriculture of New York, v. i, 1846. 



