Training of a Geologist. — Van Hise. 157 
sees, his statements will be of the most general kind and may 
be largely erroneous. The experienced geologist with a know- 
ledge of the principles of physics and chemistry and biology 
interprets the phenomena imaged in terms of these subjects. 
The engraving on his retina is the same as that of a child, but 
his brain perceives the special parts of the picture of interest 
to him in their true proportions. He understands what is im- 
portant, what is unimportant. He must select and record the 
things which are important. If he attempted to record all that 
imaged in his e}'e, a notebook would be filled with the phen- 
omena to be described at a single exposure, and yet half the 
story would not be told. Good descriptive work is discrimina- 
tive. Good descriptive work picks out certain of the facts as of 
great value, others of subordinate value, and others of no val- 
ue for the purposes under consideration. How then can this dis- 
discrimination be made. How can the facts be selected which are 
of service? Only by an insight into the causes which may have 
produced the phenomena. Without this \nsight to some ex- 
tent at least a description is absolutely valueless. So far as 
the geologist has such insight, his description is valuable. 
It is frequently urged in opposition to the above that, Tf 
a person has theories in reference to the phenomena which he 
observes his descriptions \\ill be erroneous ; he will be biased 
by his theories.' Unfortunately m many cases this is so; but 
just so far as it is true, the man fails of the qualities which 
make a successful geologist. One's theories undoubtedly con- 
trol in large measure the selection of the phenomena which are 
to be noted, and the wisdom of the selection is a certain cri- 
terion of th.e grade of the geologist. But whatever the facts 
selected for record, the statement of them should be absolutely 
unbiased by the theories. Invariably, good practice requires 
that the statement of facts and the explanation of these facts 
shall be sharply separated. Doubtless each geologist who is lis- 
tening has at different times had different ideas about the same 
locality, or while awa}- from a locality a new idea has come as 
to the meaning of the phenomena there observed. Upon re- 
turning to the old locality with the new idea, additional obser- 
vations of value have been made. But all the statements of facts 
at the previous visits should be found to be absolutely true. In 
so far as they are untrue, the geologist fails of accuracy, the 
