226 WAITMAN CROSS 
the fact that fossils may be necessary to ‘identify ” this Ztho- 
logic unit is evidence of the entrance of other ideas than those of 
lithologic characters into the underlying conception of the forma- 
tion. Stratigraphic position, continuity—giving it structural 
importance—and something of age, relatively or absolute, are 
clearly there but unexpressed. 
The writer’s conception of the geologic formation is the 
broad and general one, commonly entertained before the 
restricted use of the word ‘‘formation”’ was advocated—and 
still held, he is happy to believe, by many geologists; it is of 
something entirely unsystematic. The known portion of the 
earth consists of rock masses of various modes of origin, in 
which the record of earth history lies. In considering the 
geology of any portion of the earth, one naturally separates 
these rock masses into individuals or groups, large or small, for 
the purpose of deciphering or expressing geology. Each division 
possesses a certain unity varying in degree or kind according to 
the point of view. All but the broadest divisions may be 
properly called geological formations. 
Each rock mass assuming importance from the geologist’s 
standpoint stands for many things. It may be viewed from a 
narrow standpoint and considered to have individuality from the 
factors of that standpoint only. The lithologic characters may 
be taken into account and then it is ‘‘a lithologic individual;” 
its faunal contents considered, it may possibly be correct to 
speak of it as ‘fa faunal unit;’’ but when it is spoken of as 
a geologic formation, there should be involved the entire 
geologic record it contains. Only when the student considers 
it in its entirety is he entitled to call himself a geologist ; other- 
wise he is but a specialist —a paleontologist, a lithologist, a 
stratigrapher, or a physiographer. The writer understands the 
geological map to be a representation of certain geologic forma- 
tions, selected to express, so far as cartographic limitations per- 
mit, the geology of the area covered. 
The writer will use the term ‘‘geologic formation”’ in its 
broad sense and, in courtesy to his colleagues, consider that 
