570 The American Naturalist. [July. 
with questions of constructive and destructive processes, and with 
composition and fossil contents of rock's to be awake to another 
large question. The study of the form of the earth's surface, even 
though recognizing that the form changes, is geography. But 
after all, geography and geology are one science, treating of the 
earth, and it is needless for us to embarrass our work by attempt- 
ing unnecessary subdivision and limitation of the fields that the 
two branches shall occupy. Let each one take whatever will aid 
its attainment of the desired end. If we can understand geo- 
graphical morphology better by some consideration of geological 
structure, let it be introduced, just as chemistry is introduced into 
physiology, or physics into meteorology. Surely geologists have 
employed geographical methods freely enough to warrant our 
reversing the relation. If some consideration of geological pro- 
cesses will serv^e our purpose and give better appreciation of the 
sequence of forms that geographical individuals pass through, 
then call freely on geology for such consideration and use it to 
the best advantage. Do not hamper our endeavor to understand 
the form of the earth's surface by any arbitrary limitation of the 
means that we shall employ to the end. It is plainly apparent 
that geology and geography are parts of one great subject, as 
ancient and modern history are, and they must not be considered 
independently. Indeed, it is only in this close relation that a 
satisfactory definition of the two terrestrial sciences is obtained. 
Mackinder has concisely said that geology is the study of the 
past considered in the light of the present, and geography is the 
study of the present considered in the light of the past. I can 
quote no better indication of the close connection of the two 
divisions of the world's history. Without going further into ab- 
stract considerations, we may now turn to our concrete examples. 
The so-called "valley" of the Red River of the North in 
Minnesota and Dakota is a broad plain of exceedingly level 
surface. It is so truly level that it illustrates the curvature of 
the earth, in the same way that it is seen at sea ; for in crossing 
the plain first a distant tree-top is seen above the horizon, then a 
house-top, and at last the body of the house rises into full view; 
just as the upper and lower sails and the hull of a ship are 
