BTRATIGRAPHIC CLASSIFICATION DIASTROPHIC CRITERIA 443 



remains that can not be recognized in the limestone and shale deposits 

 farther east, while differences are noted again in comparing the faunas 

 of the latter. The second is expressed, first, by peculiarities in the 

 succession of the various general types of sediments, which on comparing 

 local sections may be arranged into four groups, and, second, by the 

 degree of metamorphism to which the deposits have been subjected. 

 The third component of the evidence is the physical proof of excessive 

 folding and overthrusting shown by the structure of the various rock 

 masses. 



Going eastward from the Adirondack areas of Precambrian crystal- 

 lines, we see, first, the Chazy basin sediments in the Champlain Valley. 

 The stratigraphic sequence in this basin is Potsdam sandstone. Little 

 Falls dolomite, three Beekmantown limestone formations, three Chazyan 

 limestone formations, Lowville and later limestones of the Black River 

 group, Jacksonburg limestone, and, finally, Martinsburg shale. Most of 

 these formations are filled with fossils, segregated into distinct associa- 

 tions, by which the formations or zones of which they are characteristic 

 are recognized in the Appalachian Valley to the south of New York, as 

 well as in different parts of the Champlain Valley. 



East of the Chazy basin is the Levis channel. In eastern New York 

 its most characteristic deposits are (1) shales and shaly, often conglom- 

 eratic, limestones, constituting the Canadian (Levis shale) part of the 

 sediments in this trough and characterized by the Dictyonema flahelli- 

 forme, Tetragraptus, and Didymograptus hifidus faunas, and (2) the 

 Normanskill and Magog shales, containing later well defined Ordovician 

 graptolite faunas. In Canada it may be that other formations (Lauzon 

 and Sillery) were laid down in this channel, but in view of the fact that 

 these formations are separated from the graptolite-bearing shales by fault 

 planes, it seems advisable provisionally to exclude them from the Levis 

 channel. The lower Cambrian deposits at Saint Albans and Georgia, in 

 northwestern Vermont, are more lil<:ely to belong here beneath the Levis. 

 As to the typical deposits of this channel, they have been recognized at 

 widely separated intervals by graptolites characterizing one or another of 

 the zones all the way from Jutland, New Jersey, to Newfoundland. In 

 the south a similar channel containing the Normanskill fauna is indicated 

 at intervals along the eastern border of the Appalachian Valley from 

 northern Virginia to central Alabama. The zone containing this grapto- 

 lite fauna in the south is included in the Athens shale of east Tennessee. 



The third trough east of the Adirondacks and Hudson River contains 

 the marble formation in western Vermont and succeeding limestone and 



