r>40 NBW YORK STATE MUSEUM 



tive fanuaa and the litbologic character of the deposits in the 

 twin rliannels are so different that we can not doubt the thor- 

 ou«j:h I'fffctiveness of the Quebec barrier during the whole of 

 Chazy tiii.e. 



i^grap't^s"' '^^ th. close of the Chazy the northwest channel, and per- 

 haps the Levis channel as well, was drained. This emerg- 

 ence continued in the Chazy basin till Black river time, 

 but, if the drainage occurred simultaneously in both chan- 

 nels, appears to have been of briefer duration in the Levis 

 channel. On tlie other hand, it seems very likely that 

 the Chazy bay was emptied sometime in advance of the Levis 

 channel, allowing deposition in the latter of beds holding the 

 lower Dicellograptus and Agnostus, Ampyx, Aeglina and Pate- 

 rula fauna, which is common to Europe and the Levis channel. 

 The earlier emergence of the Chazy channel is rendered very 

 ])lausible if we assume a period of compression at the close of the 

 Chazy, causing the strata in the western channel to be pushed up 

 on the sloping Adirondack and Laurentian masses beneath them, 

 and high enough to empty the western channel but not the Levis 

 channel. The ^ame assumption would explain the development 

 of the supposed barrier, referred to a page or two farther on, 

 across the mouth of the Ottawa arm of the Chazv bav, which, 

 if it ever existed, must have arisen about this time. 



The deposits and fauna of the supposed lower Dicellograptus 

 zone in the Levis channel are now known chieflv, if not solelv, 

 from limestone pebbles and boulders preserved in the conglom- 

 eratic horizon at the base of the Normans kill shale, the bed 

 itself possibly being now entirely covered by overthrust Cambric 

 rocks. The fauna contained in these pebbles, ns worked out by 

 Ruedemann,! contains species indicating some communication 

 with the Mississipi>ian sea in the vicinity of Albany N. Y.; or it 

 may be that the sea of the Normans kill shale, which trans- 

 gressed farther westward, also washed surfaces laid down by 

 Jilack river and early Trenton seas. 



Normans kill The Normaus kill shale, which, as we have iust said, trans- 



shale ' ' J > 



gressed a little farther west, also extended farther southward 

 'N. Y. state mus. Bui. 42. 1001; Biil. 40. 10O2. p. 89-94. 



