It's Darwin Day! Celebrating Darwin's birthday is a lot of fun, and if you know the right skeptic's group, there may be cake. With dinosaurs!

But the reason why many Darwin Day celebrations give me a small sad is because so many people forget that Darwin wasn't just a biologist. He was a geologist, too! Sure, he became known mainly for the decades of painstaking work and observation that let to On the Origin of Species by Means of Natural Selection. He revolutionized biology - no mean feat, that! But he loved geology, explored it avidly, wrote many books and papers on the subject, and said one of the most beautiful things ever about it. So, yeah. Definitely one of us.

I shall now give you a small selection of my favorite quotes on geological matters from a man who wasn't only a ground-breaking scientist, but a skilled wordsmith.

"I find in Geology a never-failing interest; as it has been remarked, it creates the same grand ideas respecting this world which Astronomy does for the Universe."

-Letter to Charles Whitley, 1834

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A bad earthquake at once destroys the oldest associations: the world, the very emblem of all that is solid, has moved beneath our feet like a crust over a fluid; one second of time has conveyed to the mind a strange idea of insecurity, which hours of reflection would never have created.

We may confidently come to the conclusion, that the forces which slowly and by little starts uplift continents, and that those which at successive periods pour forth volcanic matter from open orifices, are identical.

The appearance of the Andes was different from that which I had expected. The lower line of the snow was of course horizontal, and to this line the even summits of the range seemed quite parallel. Only at long intervals, a group of points or a single cone, showed where a volcano had existed, or does now exist. Hence the range resembled a great solid wall, surmounted here and there by a tower, and making a most perfect barrier to the country.

On January the 15th we sailed from Low's Harbour, and three days afterwards anchored a second time in the bay of S. Carlos in Chiloe. On the night of the 19th the volcano of Osorno was in action. At midnight the sentry observed something like a large star, which gradually increased in size till about three o'clock, when it presented a very magnificent spectacle. By the aid of a glass, dark objects, in constant succession, were seen, in the midst of a great glare of red light, to be thrown up and to fall down. The light was sufficient to cast on the water a long bright reflection. Large masses of molten matter seem very commonly to be cast out of the craters in this part of the Cordillera. I was assured that when the Corcovado is in eruption, great masses are projected upwards and are seen to burst in the air, assuming many fantastical forms, such as trees: their size must be immense, for they can be distinguished from the high land behind S. Carlos, which is no less than ninety-three miles from the Corcovado. In the morning the volcano became tranquil.

The rivers which flow in these valleys ought rather to be called mountain-torrents. Their inclination is very great, and their water the colour of mud. The roar which the Maypu made, as it rushed over the great rounded fragments, was like that of the sea. Amidst the din of rushing waters, the noise from the stones, as they rattled one over another, was most distinctly audible even from a distance. This rattling noise, night and day, may be heard along the whole course of the torrent. The sound spoke eloquently to the geologist; the thousands and thousands of stones, which, striking against each other, made the one dull uniform sound, were all hurrying in one direction. It was like thinking on time, where the minute that now glides past is irrecoverable. So was it with these stones; the ocean is their eternity, and each note of that wild music told of one more step towards their destiny.

-Voyage of the Beagle

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About thirty years ago there was much talk that geologists ought only to observe and not theorise; and I well remember some one 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!

-Letter to Henry Fawcett, 1861

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But Geology carries the day: it is like the pleasure of gambling, speculating, on first arriving, what the rocks may be; I often mentally cry out 3 to 1 Tertiary against primitive; but the latter have hitherto won all the bets.

-Letter to W. D. Fox, 1832

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During my second year at Edinburgh I attended Jameson's lectures on Geology and Zoology, but they were incredibly dull. The sole effect they produced on me was the determination never as long as I lived to read a book on Geology, or in any way to study the science. Yet I feel sure that I was prepared for a philosophical treatment of the subject; for an old Mr. Cotton, in Shropshire, who knew a good deal about rocks, had pointed out to me two or three years previously a well-known large erratic boulder in the town of Shrewsbury, called the "bell-stone;" he told me that there was no rock of the same kind nearer than Cumberland or Scotland, and he solemnly assured me that the world would come to an end before any one would be able to explain how this stone came where it now lay. This produced a deep impression on me, and I meditated over this wonderful stone. So that I felt the keenest delight when I first read of the action of icebergs in transporting boulders, and I gloried in the progress of Geology.

-Charles Darwin: His Life in an Autobiographical Chapter, and in a Selected Series of His Published Letters

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I cannot say how forcibly impressed I am with the infinite superiority of the Lyellian school of Geology over the Continental. I always feel as if my books came half out of Lyell’s brains & that I never acknowledge this sufficiently, nor do I know how I can, without saying so in so many words—for I have always thought that the great merit of the Principles, was that it altered the whole tone of one’s mind & therefore that when seeing a thing never seen by Lyell, one yet saw it partially through his eyes.

-Letter to Leonard Horner, 1844

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St Jago is singularly barren & produces few plants or insects.—so that my hammer was my usual companion, & in its company most delightful hours I spent.

I look forward to the Geology about M[onte] Video — as I hear there are slate there, so I presume in that district I shall find the junction of the Pampas of the enormous granite formation of Brazils. — At Bahia the Pegmatite & gneiss in beds had same direction as observed by Humboldt prevailing over Columbia, distant 1300 miles: is it not wonderful?

-Letters to J.S. Henslow, 1832

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You will have heard an account of the dreadful earthquake of the 20th of February. I wish some of the Geologists who think the Earthquakes of these times are trifling could see the way the solid rock is shivered In the town there is not one house habitable; the ruins remind me of the drawings of the desolated Eastern cities.— We were at Baldivia at the time & felt the shock very severely. The sensation is more like that of skating over very thin ice; that is distinct undulations were perceptible. The whole scene of Concepcion & Talcuana is one of the most interesting spectacles we have beheld since leaving England.

-Letter to J.S. Henslow 1835

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[Y]our references only seem to say “I cant tell you all in this work, else I would, so you must go to the Principle,” & many a one, I trust, you will send there, & make them like me adorers of the good science of rock-breaking. You see I am in a fit of enthusiasm; & good cause I have to be, when I find, you have made such infinitely more use of my journal than I could have anticipated. I will say no more about the book, for it is all praise.— I must, however, admire the elaborate honesty with which you quote the words of all living & dead geologists.

-Letter to Charles Lyell, 1838

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You can learn much more about Charles Darwin's geological work by visiting The Darwin Correspondence Project. Many of his works are available for free at Project Gutenberg, so you can read for yourself his reports on his geological observations. Happy Darwin Day!