216 The American Geologist. April, isoo 
When, then, in 1847, Logan began the examination of the 
belts of crystalline and unerystalline rocks from the frontier 
of Vermont to the vicinity of the city of Quebec, he framed 
no new hypothesis, but adopted without question, the views of 
Mather, Hall, Adams and Rogers as to the post-Trenton age 
of the unerystalline sediments, In like manner he accepted 
unhesitatingly Mather's hypothesis of their stratigraphical 
equivalence with these of the crystalline schists of the Green 
Mountain range, sustained as it Avas by the approval of the 
Messrs. Rogers and of C. T. Jackson. Logan, constitutionally 
diffident, and venturing in a new field, Avas disposed to defer 
to those Avhom he, like myself, his young assistant in the cam- 
paigns of 1847-49, had been taught to regard as authorities not 
to be questioned. Hence it was that the limestones and argil- 
lites ofPointe Levis Avere described as Hudson-River group; 
supposed to be younger than the Trenton limestone of Beau- 
port, Avhile the great mass of 2000 feet of Sillery sandstone, ap- 
parently overlying these, was regarded as the equivalent of the 
Oneida or ShaAvangunk sandstone and conglomerate of New 
York ; as may be seen in the little colored map in the Equisse 
Geologique du Canada published in Paris in 1855. The crystal- 
line rocks adjacent to the south and east were in like manner 
designated as Altered Hudson-River group. The doctrine of re- 
gional metamorphism being then taken for granted, and at the 
time scarcely questioned, I sought for proof of it alike in the field 
and in the laboratory, and found in the composition of certain 
detritalbeds near the crystalline schists, then regarded as 
beds of passage, evidence apparently confirming the meta- 
morphic hypothesis. 
Li the views of his masters, then implicitly accepted, Logan 
made in his life-time only a single change, one forced upon 
him by the results of the paleontological studies of Billings, 
which showed that the so-called Hudson-River group at Pointe 
Levis Avas really, as Eaton and, in his later view, Emmons had 
maintained, not post-Trenton in age, but pre-Trenton, and be- 
longed to the First GravAvacke of Eaton. It is unnecessary 
to remind the reader that subsequent researches have shown 
the same to be true of the greater part of the sedimentary 
rocks in question from the valley of the St. Lawrence to 
that of the Hudson. 
Logan's first acknowledgement of this conclusion Avas in a 
