114 NEW YORK STATE MUSEUM 



Doctor Ulrich distinguishes five different Eopaleozoic troughs, 

 going east from the Adirondacks, first, the Chazy basin, then the 

 Levis channel, a third trough which contains the marble forma- 

 tion in western Vermont and succeeding limestone and shale for- 

 mations, and possibly the Lower Cambric (Georgian) deposits. 

 The fourth trough is supposed to have contained the Lower Cam- 

 bric deposits, and a fifth trough, or rather set of troughs, is thought 

 to be indicated by the highly metamorphosed Paleozoics found 

 to the east of the Lower Cambric outcrops. The evidence on 

 which Ulrich bases his belief in the existence of these troughs 

 is threefold: (i) the differences in fossil contents of the sets of 

 beds; (2) the peculiarities in the succession of the various gen- 

 eral types of sediments; and (3) the physical proof of excessive 

 folding and overthrusting. 



We have in the two sheets here described undisputable evi- 

 dence of at least two parallel troughs in the two entirely differ- 

 ent sets of formations described above. These are the lower 

 Mohawk trough in the west and the Levis trough in the east. 

 If the Georgian and Bald mountain rocks belong to the third or 

 fourth trough, this is also represented on the map. We have here 

 considered them as underlying the rocks of the Levis trough, as 

 they probably do, at St Albans and Georgia in Vermont (see Ulrich, 

 op. cit., page 493). It can not be doubted that the present posi- 

 tion of the Georgian beds on the Schuylerville sheet above the 

 graptolite beds of the Levis channel, and again the position of the 

 latter above the beds of the Western basin require for the 

 explanation of this complicated reversed position under the as- 

 sumption that they represent but two troughs, a reversed anti- 

 clinorium with axial overthrust, as assumed by the writer in a 

 former publication (Bulletin 42), or a complicated system of over- 

 thrusts and that the assumption of the original deposition of the 

 Georgian beds in a third trough, which now has become pushed 

 upon the second, will considerably simplify the history of dias- 

 trophic processes which have led to the present structure of the 

 region. 



The cause of these far-reaching overthrust phenomena which 

 are observed in the whole Appalachian system is the pressure at- 

 tributed to deep-seated " suboceanic spread " which results from the 

 greater density of the terrestrial crust under the oceanic basins. 



