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IOWA ACADEMY OF SCIENCES. 
connected whole a number of views which have long been 
known, somewhat vaguely as a rule, perhaps, yet which are in 
fact, to a certain degree at least, the real foundation of 
systematic geology. It is the christening of the scheme with a 
title in which the governing causes of sedimentation are recog- 
nized, in which the elements rendering possible any systematic 
arrangement are brought into due prominence, and in which an 
old principle is greatly extended in its application, and is 
relieved of much of that which has so long overshadowed it. 
In general geological classification, about the only attempt in 
which the orotaxial principle has shown itself in the past, 
is in demarkation of the grand divisions or systems, and the 
events are commonly referred to as geological revolutions. 
The nearest approach to the practical application of the idea, in 
some of its phases, has been by Irving,* in his work on 
the pre-Cambrian crystallines of the Northwest, in which 
unconformities are given great prominence; by McGee, f in 
his investigations of the coastal plain deposits of the middle 
Atlantic slope, in which similarity of origin, or homogeny, is 
the governing factor; and by Davis + and others in their physi- 
ographic work, in which periods of base-leveling are made the 
all-important features in the cycles of land degradation and the 
consequent sedimentation in adjoining seas. 
CONCLUSIONS. 
Proceeding upon the suggestions that have just been made, 
the principles of general correlation may be more clearly shown 
by the construction of a chart (plate vi) representing a section 
across the North American continent, in an east and west 
direction, as for instance from Richmond to San Francisco. In 
a diagrammatic representation of this kind, the geographic 
provinces are cut off by vertical lines, and the geological 
systems by horizontal ones, the latter being separated by dis- 
tances approximately proportional to the estimated time inter- 
val. The skeletal chart stands for continuous and uninter- 
rupted geological history of the continent and the stratigraphi- 
cal succession from the earliest to the latest formations. In 
the proper places are indicated some of the principal physical 
*U. S. Geol. Sur., 7th Ann. Kept., p. 378, 1888. 
+Am. Jour. Soi., (3), Vol. XL, pp. 36-41, 1890. 
$Nat. Geog. Mag., Vol. I, pp. 183-253, 1889. 
