560 NEW YORK STATE. MUSEUM 



Hand in hand with this eastward decrease in the thickness of 

 the limestone is a rapid increase in the thickness of the Utica and 

 liorraine shales. While the combined thickness of Utica and Lor- 

 raine shales in a well at Rochester, Monroe co., amounted to only 

 598 feet, the two formiations were found to measure at Chitten- 

 ango, 32 miles west of Utica, 233 and 640 feet respectively (46). 

 Walcott reports a thickness of 710 feet for the Utica shale at 

 Utica; and in the section along Morphy creek to the top of 

 AdebaihiT hill between Oranesville and Amisterdam, Prosser (56: 

 €49) found 1160 feet (the Trenton limestone measures there only 

 21 feet). In the well-boring at Altamont (37) 3475 feet of shale 

 between the Upper Siluric and Trenton limestone was found; and 

 in Washington county the thickness of the " Hudson river 

 shales " has been estimated by Walcott at 5000 feet (36a). ^ 



This decrease of the Trenton limestone eastward of Trenton 

 Falls and the increase of the superjacent shales are, however, not 

 to be understood as implying that the shaly facies of the Trenton 

 limestone, specially the Normans kill shale, gradually replaces the 

 calcareous facies, for the Utica shale has been found everywhere 

 in the Mohawk valley to rest on the Trenton limestone, and the 

 Normans kill fauna is as vet unknown west of the Hudson river 

 valley; but it certainly shows that either the conditions for the 

 formation of calcareous deposits throughout Trenton time became 

 less favorable toward the east, and hence the calcareous forma- 



^The last estimates seem not to be verified by later observers. Dale (44) 

 observed the dwindling in ttie tbickness of tbe Hudson river shales in the 

 region east of tbe Hudson to "400 feet and possibly even 200 feet". This 

 phenomenon is attributed to a replacement of the shales by grits or an 

 erosion of the former before the deposition of the latter. The same cause 

 is admitted as probably explaining his low estimates (lOOO to 1200 feet) 

 for the Ordovician of the slate belt in his last paper (63:179). Kimball 

 <42) also found in Columbia county only 1285 feet of Hudson river shales, 

 but there also the series may have been reduced by subsequent erosion. 



It is to be remembered that only the Normans kill graptolites have been 

 found thus far in the above mentioned Hudson river shales and slates; 

 ^nd that, if this 1200 feet represents only the thickness of the Normans 

 kill zone, which is still to be followed by the overlying formations, middle 

 ^nd upper Trenton, Utica and Lorraine shales, this would bring the thick- 

 ness of the entire series nearer to the figure given by Ashburuer. 



