154 
IOWA ACADEMY OF SCIENCE 
a notable symposium on geologic correlation occupying the time for several 
days. This fact alone is indicative of the great interest which is being taken 
in the subject at the present time. The most suggestive paper of all, perhaps, 
was the one presented by Professor Chamberlain, of the Chicago University. 
In it was urged the use of diastrophism as an ultimate basis of geologic corre- 
lation. This is essentially the utilization of the expressions of the local changes 
in elevation or depression of the surface of the globe, particularly along the 
sea-coast, due to mountain-making and epeirogenic movements. 
Now, it may be ^of no little interest at this time to recall the fact that eleven 
years ago there was read before this Academy a paper* on this very subject. 
It was entitled “Some Physical Aspects of General Geologic Correlation.” This 
paper was a more mature consideration of an article published in the American 
Geologist three years beforet, and called “Orotaxis; A Method of Geologic 
Correlation.” Since that date I have referred on several occasions specifically 
to the subject!, particularly in treating§ of the “Orotaxial Significance of Cer- 
tain Unconformities.” 
As originally stated** the definition of orotaxis, or stratigra,phic correlation 
upon the basis of diastatic, or diastrophic, movements is essentially as follows; 
“The immediate causes for the changes between the relations of the land and 
sea areas are to be sought in orogenic and epeirogenic movements. As the two 
kinds of movements cannot be readily separated practically, and as it is of 
small advantage to separate them theoretically, the results produced may be 
all regarded as arising from the one cause — that is, from mountain-making 
forces. The greatest and most abrupt modification in sedimentation, and con- 
sequently in lithologic, faunal, and, in fact, all characters, are those connected 
directly with diastatic change, producing depression of some land areas below,< 
sea-level, and the uprising of other districts above the level at which they once 
stood, to form those great features of the earth’s surface called mountains. 
Geologic chronology, therefore, is believed to find ,a true and rational basis in 
those changes which primarily govern sedimentation and which are intimately 
connected with the genesis of mountain systems. It is proposed, therefore, 
to emphasize this factor as fundamental in the marking out of the leading 
subdivisions of geologic time and to define general stratigraphic succession in 
accordance with the cycles of orogenic development, calling the classification, 
or the fundamental principle of correlation, a systematic arrangement of 
mountains, or orotaxis.” 
By the term mountains is meant not alone those geographic features which 
at the present time rise so majestically and conspicuously above the earth’s 
surface, but also all of those remnantal structures which have been in the past ' 
prominent characters in the surface relief and which, geotectonically at least, 
are still mountains, though perhaps now completely planed off and buried be- 
neath later sediments. With these old mountains the cycles of orogenic deve- 
opment are properly regarded as extending from the time when the strata first 
were flexed, through the periods when they were bowed up, then planed ofC 
nearly to sea-level, and submerged, perhaps, until new degredational products 
*Proc. Iowa Acad. Sci., Vol. VI, pp. 131-154, 1899. 
tAmerican Geologist, Vol. XVIII, pp. 289-303, 1896. 
JSee; Science, N. S., Vol. XII, p. 146, 1900; also. Bull. Geol. Soc. America, Vol. XII, 
p. 175, 1901. 
§Am. Jour. Sci. (4), Vol. XXI, pp. 296-300, 1906. 
**American Geologist, Vol. XVIII, p. 298, 1896. 
