What is the tone of the following passage by Leander Sylvester Keyser?
In studying the birds of the West, one should note that there are
western subspecies and varieties, which differ in some respects, though
not materially, from their eastern cousins; for instance, the western
robin, the western chipping sparrow, the western lark sparrow, and the
western nighthawk. Besides, intermediate forms are to be met with and
classified, the eastern types shading off in a very interesting process
into the western. It would be impossible for any one but a systematist
with the birds in hand to determine where the intermediate forms become
either typical easterners or typical westerners.