320 J. H. BRADLEY, JR. 



On the shore of Missisquoi Bay, three-fourths of a mile north 

 of the international boundary, a group of thin-bedded siliceous 

 strata underlie the massive, apparently unbedded limestone of 

 Ai, The dip is gently to the east and the beds are conglomeratic 

 in part, with well-rounded pebbles as large as eight inches across. 

 These strata are associated in places with very thin-bedded black 

 shale. The entire thickness is less than ten feet and at the top 

 the strata grade into the calcareous rock. These beds are interesting 

 in view of Walcott's statement^ that "a small outcrop of Potsdam 

 sandstone, with characteristic fossils, subjacent to the limestone 

 qf the Calciferous" occurs on the lake shore near Philipsburg. 



These siliceous beds are the only strata similar to the outcrop 

 described by Walcott that a week's search revealed to the writer. 

 Following north along the shore, in one place three-quarters of 

 a mile south of Philipsburg, a marked unconformity was found 

 between the massive overlying limestones of Ai and the narrow 

 layers of sandstone which overlie the Champlain fault. Here the 

 sandstone dips to the east as it does farther south. The overlying 

 limestones, in this place apparently thin-bedded, meet the under- 

 lying sandstones almost at right angle, and then after bending into 

 a small anticline, resume their easterly dip parallel to that of the 

 sandstone. It is the opinion of the writer that this local difference 

 in the attitude of the strata is due purely to differential folding in 

 the two beds rather than to causes implying uplift and erosion. 



A I proper is composed of two lithologically different limestones, 

 which maintain their distinctive qualities in most of the places where 

 the members can be observed. The folded rocks mentioned above 

 are of granular nature, largely limestone, but chemically impure 

 with magnesium and mechanically impure with detrital quartz. 

 A few brown weathering, highly magnesian beds are noticeable. 

 These strata are the lowest of the series and predominantly grey 

 in color, weathering grey and brown; they will be spoken of here as 

 the grey facies of Ai. 



The beds of the grey facies are somewhat thinner than the appar- 

 ently overlying yellowish grey and buff (weathering yellow brown) 

 granular limestone. These beds will be referred to as the buff facies 



I Charles D. Walcott, Bull. Geol. Soc. Am., Vol. I, p. 512. 



