Darwin on geology and epistemology

Here is a geology quote that Michael Shermer seems to like a lot (for example, in this book). It is from a guy called Darwin:

About thirty years ago there was much talk that geologists ought only to observe and not theorize; and I well remember someone saying that at this rate a man might as well go into a gravel-pit and count the pebbles and describe the colours. How odd it is that anyone should not see that all observation must be for or against some view if it is to be of any service!