Page:The American Cyclopædia (1879) Volume VII.djvu/706

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GEOLOGY

admitted the existence of an underlying or basal system of stratified crystalline rocks, which were supposed to be anterior in their formation to the appearance of life upon the earth, and from the apparent absence of fossils were called azoic rocks (signifying without life). In accordance with this nomenclature, the formations containing the fossil remains of plants and animals have been divided into palæozoic, mesozoic, and cenozoic rocks (signifying ancient, middle, and recent life); while subsequent discoveries, indicating that life had already made its appearance in the so-called azoic period, have led to the substitution of the name eozoic (signifying the dawn of life). These four great divisions are made the basis of the accompanying tabular view of geological formations. The subordinate divisions of Cambrian, Silurian, Devonian, &c., are of local origin, which, as will be seen, is also true of the names of most of the formations into which these in their turn are divided. In regard to the palæozoic rocks, which have been most minutely studied in Great Britain and America, the names of the subdivisions recognized in these countries are given side by side. For the details of the mesozoic and cenozoic rocks, which have been made the subject of not less careful analysis and subdivision in Europe, the reader is referred elsewhere. A complete table of them is given on page 109 of Lyell's “Student's Elements of Geology” (1871).

BRITISH SUBDIVISIONS.

AMERICAN SUBDIVISIONS, WITH REMARKS.

CENOZOIC, NEOZOIC,
OR TERTIARY.

Recent

Alluvial deposits, peat bogs, &c.

Post-pliocene

Unstratified glacial drift, modified drift, &c.

Pliocene	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$
Miocene
Eocene.

Widely distributed along the eastern and southern coasts from Massachusetts to Texas, and from Nebraska across the continent to the Pacific.

MESOZOIC OR
SECONDARY.

Cretaceous.

Upper cretaceous	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$
Lower cretaceous or Neocomian

Occurs in New Jersey, Georgia, Mississippi, Arkansas, &c., and from Texas and the upper Missouri in many localities westward to the Pacific.

Jurassic.

Upper, middle, and lower oölite	$\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}$
Lias

Widely developed in the western states in various localities from Dakota and Kansas to the Pacific.

Triassic.

Upper, middle, and lower trias

Red sandstones of the Connecticut valley, New Jersey, Pennsylvania, the coal fields of Richmond, Va., and Chatham, N. C.

PALÆOZOIC
OR
PRIMARY
FOSSILIFEROUS.

Permian.

Magnesian limestone

Permian

Known in Illinois, Iowa, and Kansas.

Carboniferous.

Coal measures

Coal measures	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	To this horizon belong the coal formations of New Brunswick, Rhode Island, Michigan, Illinois, and the great Appalachian coal field.
Carboniferous limestone
Waverley

Millstone grit

Lower carboniferous

Devonian.

Upper, middle, and lower Devonian

\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \\\ \ \end{matrix}}\right.}

Catskill.

Portage and Chemung	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	The Erie division of the New York series. Hence Dawson uses Erian as synonymous with Devonian.
Upper Helderberg
Schoharie and Cauda-galli.

Silurian
(Sedgwick).

Upper and lower Ludlow

\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}

Oriskany	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$	The upper Silurian of Murchison, the third fauna of Barrande. The stratigraphical and palæontological break at the top of the Water-lime makes two great divisions of the American Silurian.
Lower Helderberg

Water-lime
Onondaga or Salina
Niagara
Clinton
Oneida and Medina

Wenlock
Llandovery or May Hill		$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$

Cambrian
(Sedgwick).

Upper.

Caradoc or Bala		$\scriptstyle {\left\{{\begin{matrix}\ \\\ \end{matrix}}\right.}$

Llandeilo

Hudson River	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	The lower Silurian of Murchison, or the second fauna of Barrande.
Utica
Trenton

Middle.

Tremadoc.

Lingula flags

Chazy	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \\\ \\\ \\\ \\\ \\\ \ \end{matrix}}\right\}\,}$	These include the primordial Silurian and the Cambrian of Murchison, the primal and auroral of Rogers, the Taconic of Emmons, and the Quebec group of Logan, and correspond to the first fauna or primordial zone of Barrande.
Levis
Calciferous
Potsdam

Braintree and St. John's
——— ?
——— ?

Lower.

Menevian

Harlech

Llanberris

EOZOIC.

Primitive crystalline schists (Urschiefer)

\scriptstyle {\left\{{\begin{matrix}\ \\\\\ \ \end{matrix}}\right.}

Norian or Labrador	$\scriptstyle {\left.{\begin{matrix}\ \\\\\ \ \end{matrix}}\right\}\,}$	Above the Laurentian, and probably in the order here given.
Montalban or White Mt
Huronian or Green Mt

Primitive gneiss (Urgneiss)

Laurentian

\scriptstyle {\left.{\begin{matrix}\ \\\ \end{matrix}}\right\}\,}

Dana uses the name Archæan as synonymous with Eozoic.

It should, however, be borne in mind that all such divisions of the rocks are arbitrary and artificial. From the mode in which sediments have been deposited, and from the alternations