Five-minute digest
Principles of Geology
Summary
Principles of Geology is Charles Lyell's argument that the earth's past can be explained by the same causes that are acting on it now, working at their present intensity over immense periods of time. The first edition appeared in three volumes in 1830, 1832 and 1833, under a subtitle describing it as an attempt to explain the former changes of the earth's surface by reference to causes now in operation. Lyell revised it repeatedly. The library text is the 1854 New York printing of the ninth edition (1853), in which, as the Preface explains, the old fourth book on the rock record had been moved to a separate Manual of Elementary Geology, so that the Principles now treat the modern changes of the earth and its inhabitants. Book I (Chapters I to XIII) opens with a history of geology from ancient cosmogonies through Arabic writers such as Avicenna, Italian students of fossils, Abraham Werner and James Hutton. Lyell argues that the science was long held back by a belief that the earth was only a few thousand years old, which forced writers to imagine sudden, violent catastrophes. He imagines Egyptologists who believed the Nile valley had been inhabited only since 1800 and shows what absurd theories they would invent to explain the pyramids. He then considers climate change, the history of life and the antiquity of man, and concludes that the assumption of a discordance between ancient and present causes discourages patient inquiry. Book II (Chapters XIV to XXXII) surveys the inorganic agents now at work. Rivers cut valleys and build deltas such as those of the Mississippi and Ganges; ice carries boulders; waves wear away the coast of England. Lyell describes the volcanoes of Naples, Vesuvius and Etna, and the Calabrian earthquake of 1783. In Chapter XXIX the frontispiece subject, the so-called Temple of Serapis at Pozzuoli, shows columns bored by marine molluscs to a height of about twenty-three feet: the ground had sunk beneath the sea and risen again within historic times, without destroying the building. Further chapters treat the slow rising of land in Sweden and the causes of earthquakes and volcanoes. Book III (Chapters XXXIII to L) turns to the living world: whether species are real and fixed, a detailed critique of Lamarck's theory of transmutation, hybrids, the geographical distribution of plants and animals, the extinction of species through competition and changing conditions, the burial of organic remains in peat, caves and sediments, and finally coral reefs, where Lyell adopts the theory of his friend Charles Darwin. Darwin carried the first volume aboard the Beagle in 1831 and later said that it altered the whole tone of his mind.
Top Lessons
The present as a guide to the past
Lyell's method is to study rivers, volcanoes and earthquakes as they act today and then ask how much they could accomplish over long ages. Small causes, he argues, become great when multiplied by time. The method still guides geologists, though they now also recognize rare large events.
Assumptions shape what we see
In Chapter V Lyell imagines scholars who believe Egypt was first inhabited in 1800 and then try to explain the pyramids. His point is that a wrong assumption about time forces every new fact into an ever more strained theory.
Reading the landscape as a document
Lyell treats rocks, shells and ruins as records written in a symbolic language. The Temple of Serapis, with its bored columns, becomes a document of the land's rising and sinking. Careful observation turns a ruin into evidence.
A science that shaped another
Darwin read the Principles on the Beagle and learned from Lyell to explain large effects by small, continuing causes. Yet Lyell himself, in this edition, argued against the transmutation of species. The book shows how a method can lead a reader beyond the author's own conclusions.
Verified Quotes
“They may be regarded, in short, as a symbolical language, in which the earth's autobiography is written.”
“Geology is the science which investigates the successive changes that have taken place in the organic and inorganic kingdoms of nature; it inquires into the causes of these changes, and the influence which they have exerted in modifying the surface and external structure of our planet.”
“Never was there a dogma more calculated to foster indolence, and to blunt the keen edge of curiosity, than this assumption of the discordance between the ancient and existing causes of change.”
“It also endeavors to estimate the aggregate result of ordinary operations multiplied by time”
“Thus, although we are mere sojourners on the surface of the planet, chained to a mere point in space, enduring but for a moment of time, the human mind is not only enabled to number worlds beyond the unassisted ken of mortal eye, but to trace the events of indefinite ages before the creation of our race”
“it is clear that the columns must have continued for a long time in an erect position, immersed in salt water, and then the submerged portion must have been upraised to the height of about twenty-three feet above the level of the sea.”
Medical Lens
Medicine appears incidentally. Lyell's account of the Calabrian earthquake of 1783 records the deaths that followed from epidemics caused by hunger, exposure and malaria from newly formed stagnant pools, reflecting the period's understanding of malaria as arising from marsh air. His discussion of the Temple of Serapis notes that the Serapis cult had taken over the healing attributes of Aesculapius and that devotees slept in the temple hoping for revelations about their diseases, a practice of incubation known from ancient medicine. In Book III he treats epidemic disease, famine and swarms of locusts as forces that can thin or extinguish animal populations. Several of the early geologists in his historical chapters, including Avicenna, were physicians.
- Book II, Ch. XXVIII
Deaths after the Calabrian earthquake of 1783 from epidemics attributed to insufficient food, exposure and malaria from new stagnant lakes.
- Book II, Ch. XXIX
The Serapis cult's healing role and the practice of sleeping in the temple to receive cures in dreams.
- Book III, Ch. XL–XLI
Epidemic disease and famine from locust swarms discussed as causes of population loss and extinction.