XV.] CAMBRIAN AND SILURIAN IN NORTH AMERICA. 413 



beds there appears to be, in North Wales, a mingling of forms 

 of the first and second faunas, as in the Levis and Chazy 

 formations. The latter was already, by Hall, in 1847, declared 

 to be beneath the Silurian horizon then recognized in Great 

 Britain ; and it is by its fauna comparatively isolated from the 

 strata both below and above it. According to a private com- 

 munication from Professor James Hall, the Chazy limestone at 

 Middleville, Herkimer County, New York, to the south of the 

 Adirondacks, is wanting, and the basal beds of the Trenton 

 group (the Birdseye limestone) there rest unconformably upon 

 the Calciferous sand-rock. 



The relations of the various members of the Quebec group 

 to each other, and of the group, as a whole, to the succeeding 

 Trenton and Hudson River groups, require further elucidation. 

 If, as I am disposed to believe, the southeastward-dipping 

 series of the older strata near Quebec exhibits the northwest 

 side of an overturned and eroded anticlinal, in which the 

 normal order of the strata is inverted, then the Lauzon and 

 Sillery divisions, which there appear to overlie the Levis lime- 

 stones and shales, are older rocks, occupying the position of 

 the Potsdam or of still lower members of the Cambrian. Sir 

 William Logan supposes the appearance of these rocks in their 

 present attitude by the side of the strata of the Trenton and 

 Hudson River groups, in the vicinity of Quebec, to be due to 

 a great dislocation and uplift subsequent to the deposition 

 of these higher rocks ; but, as elsewhere suggested (ante, page 

 263), I conceive the Quebec group to have been in its present 

 upturned and disturbed condition before the deposition of the 

 Trenton limestones. The supposed dislocation and uplift, ex- 

 tending from the Gulf of -St. Lawrence to Virginia, is, accord- 

 ing to this view, but the outcrop of the rocks of the first fauna 

 from beneath the unconformably overlying strata of the second 

 fauna. The later movements along the borders of the Appa- 

 lachian region have, however, to some extent, affected these, 

 in their turn, and thus complicated the relations of the two 

 series. This unconformity, which corresponds to the marked 

 break between the Levis and Trenton faunas, is further shown 



