I'm currently reading C. S. Lewis's Studies in Words. 

Two things particularly stand out to me as I am reading this book: first, the breadth and depth of Lewis's reading; and second, his incredible memory of what he has read. Let me give an example. In the second chapter of the book, he is discussing the different meanings of the word "nature" down through the centuries. One of these meanings is Nature personified, or "Great Mother Nature." Lewis discusses this usage in the following paragraph:

[The use of the word "nature" to refer to] Great Mother Nature has proved a most potent sense down to the present day. It is 'she' who does nothing by leaps, abhors a vacuum, is die gute Mutter, is red in tooth and claw, 'never did betray the heart that loved her', eliminates the unfit, surges to ever higher and higher forms of life, decrees, purposes, warns, punishes and consoles. Even now I am not sure that this meaning is always used purely as a figure, to say what would equally make sense without it. The test is to remove the figure and see how much sense remains. Of all the pantheon Great Mother Nature has, at any rate, been the hardest to kill. 

Lewis is referring to several famous passages on Nature from English letters--Tennyson, Wordsworth, Darwin, etc. Yet nearby this paragraph, he refers to Langland, Bernardus Silvester, Chaucer, Aristotle, Plato, Euripides, Addison, Milton, Spenser, and others. What strikes me is that Lewis is writing in a day without Google Scholar and without library databases. He is probably sitting in the Bodleian as he writes this, but much of this is off the top of his head. 

The gulf between the modern "well-read" reader (such as an English prof) and a reader like Lewis is immense. I read Lewis in awe, but love to learn from him.