Emmons on American Geology. 401 
_ and serpentines was subsequent to the deposition of the Potsdam 
_ sandstone, which he asserts is vitrified in contact with the lime- 
stone. Again, speaking of the Adirondack Mountains west of 
Lake Champlain, which belong to the Laurentian series, he tells 
us that their elevation— 
** Was probably subsequent to the consolidation of all Lower Silu- 
rian rocks. On Lake Champlain the evidences of movements of a 
much later date are fully established. * * hese movements have 
Champlain and the St. Lawrence. All that portion however of the hy- 
persthene rock, which extends to the lake has been Paised about 500 
feet since the drift period.”"—p. 77. 
The only evidence of recent eleyation upon Lake Champlain, 
where all the palaozoic strata are undisturbed, is the existence of 
marine tertiary clays 500 feet above the present sea-level, and 
incredible as it may seem, Mr. Emmons has confounded the gen- 
eral elevation of the continent since the drift period, with the up- 
lifting of the most ancient mountain system of America! 
_ With regard to his vitrified Potsdam sandstone, the fact is sim- 
ply this, that the limestones of the Laurentian series are generally 
associated with very quartzose strata, and often with pure quartz 
; rock, which constitutes an important member of the series, and is 
constantly mistaken for the Potsdam sandstone by Emmons. We 
have seen the unaltered and horizontal beds of this sandstone repos- 
| of the beds the character of a conglomerate. In connection with 
| this, we may mention an error into which the author has fallen 
| in his description of the Potsdam sandstone in his report on the 
Northern District of New York. He tells us that this rock ap- 
pears at the Falls of Montmorenci in Canada, stained green with 
opper, and resembling lithologically ‘‘the new 
red sandsone.” At this locality the Trenton limestone with its 
he tells us that the evidence 
that of primary limestone. 
| c 
| among the pyrocrystalline rocks, yet 
; of its igneous origin “is less than 
Seconp Seures, Vol. XIX, No. 57. May 1855. 
