SIXTH REPORT OF THE DIRECTOR IQ/X) 1 23 



an additional thickness of some 150 feet. Almost at the base is 

 the shaly zone with Lingulepis acuminata, first reported 

 by Shaler and H. S. Williams. 



Though the outcrops are not entirely satisfactory, there is reason 

 to believe that the unconformity at the base of the Tribes Hill 

 limestone locally descends in this vicinity to the top of the ponderous 

 Cryptozoon chert included in bed 9 of the above section. This 

 condition is suggested on the ridge just west of the creek. That 

 the floor on which the Tribes Hill was laid down was uneven is 

 shown by comparison of the two detailed sections made on the north 

 side of the river in the bluffs back of Little Falls. In the section 

 exposed in the creek on the northwest edge of the town, as above 

 described, the Tribes Hill has a thickness of about 50 feet. The 

 silicified Cryptozoon reef of the Little Falls dolomite, which seems 

 to be a persistently marked zone in this vicinity, lies here about 

 30 feet lower, hence 80 feet beneath the base of the Lowville. 

 Less than 200 feet to the west the 30 foot interval is reduced to 

 about 18 feet The basal bed of the Tribes Hill (no. 12 of section) 

 also is reduced from 30 feet to about 16 feet. In a branch of 

 this creek about 1/6 mile east, the Cryptozoon bed is only 58 feet 

 beneath the Lowville and only 21 feet beneath the base of the 

 Tribes Hill, which, therefore, is but 37 feet thick at this point. The 

 loss of 13 feet, when compared with the section in the main 

 branch of the creek, is found to be divided between the top and 

 bottom, beds 16 and 17 of that section, aggregating 5 feet, being 

 absent here. The other 8 feet probably are lost from the base, 

 though the character of the middle and lower beds of the Tribes 

 Hill varies rapidly from place to place so^ that the individual beds 

 are not easily recognizable. A mile farther east, along the road 

 to the quarries northeast of Little Falls, the Tribes Hill seems even 

 thinner, but the exposures are too poor and the dip not sufficiently 

 regular to permit a definite statement on this point. 



In mapping the Little Falls sheet it was shown that the dolomite 

 formation rapidly thinned because of overlap, in passing across the 

 quadrangle from south to north. It was at that time supposed to 

 be a single formation, and the loss by overlap was supposed to be 

 at the base. Since, however, we are dealing with two, uncon- 

 formable formations it may well be that both thin northward be- 

 cause of overlap, and that the Tribes Hill disappears before the 

 Little Falls does, letting the Lowville down upon the latter. Until 

 the quadrangle is restudied it is impossible to definitely pronounce 



