18 NSW YORK STATE MUSEUM 



upper beds with the overlying limestone are well exposed in the 

 bed of Cazenovia creek below the bridge at Spring Brook. 



TICHENOR LIMESTONE 



The stratum of limestone that succeeds the Ludlowville shale has 

 been commonly known as the " Encrinal limestone," a name ap- 

 plied to it by Hall in 1839 on account of the great abundance of 

 fragments of crinoid stems contained in it. 



Since this term has been applied by others to limestone layers 

 of similar character occurring at distinctively different horizons 

 and specially to the limestones in the lower Ludlowville beds, 

 thereby causing confusion in the identification of horizons, a more 

 distinctive appellation for this stratum was required. It has there- 

 fore been designated Tichenor limestone from its typical exposure 

 in the ravine at Tichenor point on Canandaigua lake and along the 

 shore toward the south. . It usually consists of a single compact 

 layer of bluish gray limestone, hard and durable, with a thickness 

 varying from 12 to 18 inches and continuous, with many outcrops, 

 from Onondaga county to Lake Erie, disappearing at the mouth of 

 Pike creek. 



This stratum in central New York is usually overlaid by cal- 

 careous shales, but on these quadrangles where the formation at- 

 tains its greatest development on the line of outcrop it is followed 

 by one or more layers of limestone that make the total thickness 

 of the formation about 3 feet. The Tichenor limestone carries 

 an abundant fauna. Doctor Grabau's list contains the names of 60 

 species occurring in it in this region, of which the following are the 

 more abundant and striking forms : 



Phacops rana Green 

 Diaphorostoma lineatum Flail 

 Modiomorpha concentrica Conrad 

 Rhipdomella vanuxemi Hall 

 R. penelope Hall 

 Spirifer granulosus (Conrad) 

 Sp. mucronatus Hall 

 Vitulina pustulosa Hall 

 Centronella impressa Hall 

 Cryptonella planirostra Hall 

 Tropidoleptus carinatus (Conrad) 

 Favosites hamiltoniae Hall 



Exposures. The Tichenor limestone is exposed in the lower part 

 of most of the principal ravines in the southern part of this quad- 

 rangle, and by reason of its superior resistance to the erosive power 



