12 NEW YORK STATE MUSEUM 



In volume 3, Palaeontology of Nciv York, 1859, pages 42-45, 

 the Onondaga and Coniiferous limestones, together with the 

 Schoharie grit and the Cauda-galli grit which do not extend as far 

 west as these quadrangles are classified as composing the " Upper 

 Helderberg group " and this term has been widely used, specially in 

 connection with the fauna of those beds. 



Investigations subsequent to the geological survey of 1837-42 

 have led to the conclusion that there are no well defined structural 

 changes in the character of the limestones in this formation that 

 are continuous for more than a short distance, the exceedingly 

 irregular distribution of the chert making its presence or absence 

 of no value as a guide to their stratigraphy, and the clearer sub- 

 crystalline character of the basal layers at some localities being due 

 to aggregations of corals, crinoid stems and other fossils in a man- 

 ner suggestive of coral reefs, in which the species are mainly if not 

 entirely those found to occur in greater or less abundance in the 

 higher beds. 



In the reports of the fourth and third districts for 1838 in which 

 the name Onondaga was first applied to the limestone as a unit 

 term Hall and Vanuxem also used this word as a group term to 

 designate the " Saliferous group of Onondaga," changing in the 

 report for the succeeding year to " Onondaga salt group," thus 

 duplicating the use of the word. 



In 1899 Clarke and Schuchert in a revised Classification of the 

 Nezv York Geologic Formations eliminated " Onondaga " as a 

 group term and continued it as a unit term in compliance with the 

 rules of geologic nomenclature, its application being expanded to 

 cover all of the limestone strata between the Oriskany sandstone 

 horizon and Marcellus shale, which for reasons above stated are 

 considered as constituting one formation. The name Seneca thus 

 discontinued as a unit term, has been employed as the designation 

 of a period or group (Senecan) for the formations extending from 

 the top of the Hamilton to the top of the Portage beds. 



The formation consists of a heavy deposit of limestone, very 

 dark when freshly quarried but on exposure weathering to a light 

 bluish gray color. Its line of outcrop from the Hudson river valley 

 to Buffalo is marked by hundreds of quarries that have produced 

 and are still producing enormous quantities of handsome and dura- 

 ble building stone, and valuable fluxing road material. Until re- 

 cently the manufacture of quicklime from these beds was also an 

 important branch of business. 



