22 
GEOLOGY OF THE FOURTH DISTRICT. 
“ same geological age.” From examinations made in the eastern part of Maine, New- 
Brunswick, Nova-Scotia and Canada, by Messrs. Jackson and Alger, Capt. Bayfield, Dr. 
Emmons and others ; and from the examinations of Bigsby on Lake Huron, of Houghton in 
the northern and southern peninsulas of Michigan, and of Owen upon the Mississippi river; 
together with facts collected from others, and having also passed over much of this ground 
myself, as well as of some intermediate points, it appears that there is an almost continuous 
deposit of the lower rocks of this great system entirely across the continent, from the Atlantic 
to the Pacific oceans. Thus over an extent of more than half the circumference of the globe, 
the existence of these older fossiliferous rocks has been proved ; and from being a neglected 
and unarranged mass, they seem likely to assume the first rank in importance among geolo¬ 
gists of the present day. 
Notwithstanding the remarkably persistent character of the lower formations of this great 
System, I am able to state from personal observation that the higher groups thin out rapidly 
in a western direction from New-York. The rocks above the Helderberg series, known in 
New-York as Marcellus slates, Hamilton, Portage and Chemung groups, and some minor 
subdivisions, altogether forming a mass of more than three thousand feet in thickness, have 
diminished to less than as many hundreds before reaching the Mississippi river. At the same 
time, the rocks forming the principal part of the Catskills, and being in part or the whole 
equivalent to the Old Red Sandstone of Europe, together with several members of the Helder¬ 
berg series, have disappeared in a western direction within the limits of the State of New- 
York. The wide spread and generally uniform character of the one, proves a similarity of 
circumstances throughout; while the great difference in thickness, and the absence of fossils 
in parts of the other, proves a great difference in the conditions under which they were depo¬ 
sited at different points. We shall probably find that the remark heretofore made, that “ the 
older deposits are the more universal,” will hold true, not only as regards the great systems or 
classes, but also the minor subdivisions. It exhibits in the commencement of the organic 
period, a uniformity in depth and temperature of the ocean, or other circumstances favorable 
to the development of the same forms over vast areas, which in subsequent periods have 
constantly diminished. 
While the investigations have been going on which have resulted in the development of the 
rocks of New-York, as exhibited in the tabular arrangement, we have had fellow laborers in 
other parts of this great field. Other States have pursued the same course; and from the 
numerous and efficient observers, we have accumulated a great amount of knowledge regarding 
the geological structure of the whole Union. 
In Maine, the Primary and lower fossiliferous rocks have been investigated by Dr. Jackson, 
and also the Primary and Coal measures of Rhode Island, and the Primary of New Hamp¬ 
shire. 
In Massachusetts, after the publication of the report of the first survey, a resurvey was 
ordered; and Prof. Hitchcock has just completed two quarto volumes, giving the results of 
his researches in the Primary, some isolated tracts of the Carboniferous, New Red Sandstone 
of the Connecticut valley, and Tertiary upon the coast. 
