APPLICATION OF PKINCIPLE OF TRANSGRESSIVE OVERLAP 575 



feet of limestones, shales, and intercalated sandstones carrying the Ole- 

 nelhis fauna.* 



In northern Vermont the Lower Cambric consists of over 2,000 feet 

 of limestones and shales with the Olenellus fauna, but the base of the 

 series is not exposed. Southward, in the slate belt, the maximum thick- 

 ness of the Lower Cambric is estimated by Dalef to be 1,400 feet, at 

 Hebron mountain. The base is not exposed and the upper part is 

 formed of quartzite and sandstone ranging in thickness up to 100 feet. 

 Then follows 1,000 to 1,200 feet of Lower Ordovicic, the Middle and 

 Upper Cambric series being apparently absent.^ On the flanks of the 

 Green mountains the basal Cambric beds are sandstone, resting uncon- 

 formably on the pre-Cambric gneiss. These are the granular quartz of 

 the Vermont geologists, which were long ago referred to the Potsdam on 

 account of their position. The thickness of the quartzite is estimated 

 at from 800 to 900 feet,§ and about 470 feet of the overlying Stock- 

 bridge limestone is also referred to the Lower Cambric. || This makes a 

 total of 1,370 feet for the maximum of the Lower Cambric in the Green 

 Mountains section. Compared with the Highgate Springs section, the 

 base of the Green Mountains section seems to be considerably higher in 

 the column, since in the northern Vermont section the basal beds are not 

 shown. Walcott has suggested that the great mass of argillite east of 

 the Vermont Central Eailroad track in the Georgia section may be older 

 than the limestone at the base of the section.^ If this is the case, the 

 Vermont section becomes more than double the thickness now assigned 

 to it. In any case it is likely that the basal granular quartz of the Green 

 Mountains is the time equivalent of the upper portion of the limestones 

 of northwestern Vermont. 



Southern Appalachian area. — The Hardyston quartzite of New Jersey 

 represents the basal member of the series in the northern part of the 

 southern Appalachians. It rests on the pre-Cambrics of the Highlands 

 and varies from a few feet to over 200 feet, probably owing to the irreg- 

 ularity of the pre-Cambric floor.** It is often feldspathic and occasion- 

 ally a conglomerate. It frequently grades up into the overlying Kit- 

 tatinny limestone, which has an estimated thickness of from 2,700 to 



* Murray : Geological Survey Rept. of Newfoundland, 1864. 



f Nineteenth Ann. Rept. U. S. Geological Survey, pt. iii, p. 178. 



t This appears to be true of the Middle Cambric in the northern Vermont region, 

 though coarsely conglomeratic limestones with Upper Cambric fossils occur here. On 

 the whole it seems that the northern Appalachian trough was dry land during Middle 

 Cambric time, the sea returning only in Upper Cambric time. 



§ Pumpelly, Wolf, and Dale : Monograph 23, U. S. Geological Survey, 1896, p. 190. 



|| Dale : Fourteenth Ann. Rept. U. S. Geological Survey, 1895, p. 541. 



If Bulletin 30, U. S. Geological Survey, 1886, p. 19. 

 ** Weller : Paleontology of New Jersey, vol. iii. 



