374 NEW YORK STATE MUSEUM 



conditionsi there.^ In the Cliamplain valley they are more 

 limited to the basal portion; of the formation than is the case 

 along the Mohawk. 



In the lower Ohamplain region the writer know® of no con- 

 tinuous section of the Trenton, and its thickness there is largely 

 a matter of conjecture. A minimum limit may be assigned, but 

 no maximum, and there are beds, apparently Trenton, whose 

 stratigraphiic horizon is yet unknown. In the bed 'of the Little 

 Chazy river, at Chazy village, the lower 150' feet of the formation 

 are shown, directly overlying the Black River beds, and consist- 

 ing at the base of slaty layers, alternating with beds of hard, 

 brittle, blue black limestone; the major portion of the section 

 being however constituted of the limestone, the slaty layers 

 vanishing, and in this portion are occasional layers of the gray, 

 crystalline limestone which are masses of fossils. 



Along the lake shore northward from Bluff point, Trenton rocks 

 outcrop continuously for ^ mile, being separated from the Chazy 

 limestones which constitute the point by a fault. Because the out- 

 crop surface is horizontal, and the dip varies much in amount 

 and diirectiom, it is a difficult section to measui'© accurately, but 

 a thickness of at least 100 feet is involved. At the base are many 

 of the coarse gray, fossiliferous layers, but these die out toward 

 the summit, and the rock becomes shaly. This section seems to 

 overlap, in part, tlfe section at Chazy, but to show higher beds 

 than an}^ seen there. 



On Crab island, a mile northeast from Bluff point, out in the 

 lake, an excellent Trenton section is exposed which is practically 

 a continuous one. The exposures comprise part of a low, north- 

 erly pitching anticline, the island is nearly a half mile long, and 

 the writer has estimated the thickness of the section at 200 feet. 

 Brainard and Seeley state the thickness to be over 200 feet, and 

 the writer is confldeut that White's figure of less than 100 feet 

 falls far short of the truth.^ The lower part of the section, at the 

 south end of the island, shows much of the gray, crystalline, 

 fossiliferous limestone. Following this are thin bedded, slaty 

 layers, but the upper part of the section, comprising more than 



'Geol. Soc. Am. Bui. 10:455. 



^Gushing, H. P. 15th An. Rep't State Geol. p.514; Brainard & Seeley. 

 Am. Mus. Nat. Hist. Bui 8 :308 ; White, T. G. Geol. Soc. Am. Bui. 10 :457. 



