378 NEW YORK STATE MUSEUM 



Coming westward, at Tribes Hill, a measured 40 feet of Trenton 

 is the section record, and it terminates in the formation, so that 

 the actual thickness ma}^ be somewhat greater. At the base is a 

 12 foot thickness of massive, dark blue limestone, with some 

 crystalline lenses, followed hj 11 feet of thin bedded, uneven, gray 

 crystalline and dark colored limestones, which are capped by 17 

 feet of thin bedded, uneven, dark blue limestone. 



At Spraker the formation has thinned to 17 feet, both con- 

 tacts showing, and consists of thin layers of dark blue limestone, 

 apparently representing the upper part only of the Tribes Hill 

 section and with the Lowville and Black Eiver both lacking as 

 well. Three miles west, at Canajoharie, the thickness and litho- 

 logic character are the same, and here the unconformity between 

 the Beekmantown and Trenton is also plainly marked by a dis- 

 cordance in dip [pl.7] . 



In the district about Little Falls the formation shows con- 

 siderable variation in thickness, with rapid increase westward. 

 On East Canada creek it is about 50 feet thick, with the Lowville 

 always, and the Black River sometimes appearing beneath. Here 

 it consists largely of gray, crystalline, fossiliferous layers, these 

 being capped by thin bedded, blocky, black limestones, which 

 become intercalated with shales and grade into the Utica above, 

 the distinctive passage beds being of about the same thickness 

 as the ordinary Trenton. 



At Little Falls Prosser has assigned 104 feet to the formation, 

 though but little of it is exposed in his section. The writer's 

 measurements north of that point show an average of 80 feet of 

 thickness, with again an equal amount of passage beds above. 



Along West Canada creek, between Herkimer and Middleville, 

 the Trenton ranges from 100 feet to 120 feet in thickness, the 

 gray, crystalline, thin bedded type largely predominating in the 

 lower half of the section and the dark colored type in the upper. 

 Here also is an approximately equal thickness of passage beds, 

 alternate shale and limestone layers, the limestone being identical 

 in character with the dark colored Trenton type, and the shale 

 being indistinguishable from the ordinary Utica. 



. Northward from Middleville there are man}^ exposures of the 

 Trenton, but most are of merely the lower portion, and there is 



