136 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
conformably on the altered strata of the Quebec {i;roiip; and at 
Montreal, where the Lower Helderberg overlies iinconformably 
the Hudson beds." 
After thirty years, the accumulation of knowledge about the 
structure of eastern North America led Dana to elaborate 
the orijj^inal ideas in the following words. "The strata of the 
Low(T Silurian in eastern North America appear to have been 
laid down, one over the other, without intervening dislocations. 
. . . Mountain-making finally ensued, producing, among its 
efifects, the Taconic Mountain Range along western and north- 
western New England, and also the Cincinnati geanticline, be- 
sides uplifts in Nova Scotia and New Brunswick. Moreover, 
there is probable evidence that the Taconic Range at the north 
was but one of a series along the Atlantic border. . . . The 
Taconic upturning is known to have occurred not later than the 
close of the Lower Silurian era from the fact that Upper Silurian 
rocks are not present in the series, but actually overlie the Lower 
Iinconformably in some localities; . . . The probability that 
the upturning was continued southward through Virginia has 
been sustained by the discovery, in 1892, of Crinoids, by N. H. 
Darton, in the slate quarries of Arvon, Buckingham County, 
Va. . . . Walcott states that the species . . . are of either 
Trenton or Hudson age. . . . Unconformability between the 
Upper Silurian and the Lower Silurian rocks has been observed 
in Carleton County, N. B., just north of the boundary near 
Metapedia Lake, and also on Lake Temiscouata, and elsewhere 
(L. W. Bailey) ; and in Nova Scotia at Cape St. George, Arisaig, 
Lochaber, and from Kerrowgane down the East River of Pictou, 
and north of Sunderland Lake."^ 
It has long been granted that in the formative period of 
American geology no other book exerted as much influence 
upon the growth of the science as Dana's Manual. Since its 
last edition in 1895, its influence has naturally diminished, but 
could the same hand that wrote it now revise it in the light of 
modem knowledge and progress it is probable that its superiority 
would remain unchallenged. One cannot read an up-to-date 
text-book without recognizing its debt to the Manual, and this 
>Dana, J. D. Manual of Geology. Fourth ed., p. 526, 1895. 
