But another discipline was in the process of formation that would put history, and in particular pre-history, on to a different footing and further prepare the way for Darwin – this was geology. Geology differed fundamentally from all the other sciences, and from philosophy. It was, as Charles Gillispie has said, the first science to be concerned with the history of nature rather than its order.
In the seventeenth century Descartes had been the first to link the new astronomy and the new physics to form a coherent view of the universe, in which even the sun – let alone the earth – was just another star. He speculated that the earth might have formed from a ball of cooling ash and become trapped in the sun’s ‘vortex’. (To avoid criticism from the Church, he said only that this ‘might’ have happened.) Bernard de la Fontenelle, in A Plurality of Worlds (1688), had stressed man’s insignificance in the new order of things, and had even wondered if other stars might be inhabited.23 The idea that physics operated on the same principles throughout the universe was a major change in thinking that could not have occurred to the medieval mind. The basic ideas of heaven and earth, as understood in the West at least, were Aristotelian and the two realms were held to be fundamentally different: one could not give rise to the other.24 Eventually, Descartes’ physics were replaced by Newton’s, the ‘vortex’ with gravity, but that didn’t alter early geological theories very much. In 1691 Thomas Burnet published his Sacred Theory of the Earth, in which he argued that various materials had coalesced to form the earth, with dense rock at the centre, then less dense water, then a light crust, on which we live. This conveniently explained the Flood – just beneath the thin crust were vast tracts of water. A few years later, in 1696, William Whiston, Newton’s successor at Cambridge, proposed that the earth could have been formed from the cloud of dust left by a comet, which coalesced to form a solid body, and was deluged with water from a second passing comet.25 This idea, that the earth was once covered by a vast ocean, which then retreated, proved enduring. G. W. Leibniz added the thought that the earth had once been much hotter than it is now, and that earthquakes would therefore have been much more violent in the past. (Even then it was clear that present-day earthquakes had very trivial effects on the surface of the earth.)
In the eighteenth century, in his ‘nebular hypothesis’, Kant proposed that the entire solar system was formed from a condensing cloud of gas, a theory that received support from the observations of William Herschel, whose vastly improved telescopes showed, or appeared to show, that some of the nebulae ‘or hazy patches’ seen in the night sky were gas or dust clouds ‘apparently condensing into a central star’.26 Buffon built on this, but like Descartes before him he too sought accommodation with the church, arguing that the earth started out as very hot, but cooled in seven phases (analogous to the seven days of the week in biblical creation), the last of which gave rise to man.
Slowly, then, a view was forming that the earth itself had changed over time. Nonetheless, however the earth had formed, the central problem faced by the early geologists was to explain how sedimentary rocks, formed by deposition from water, could now stand on dry land. As Peter Bowler has pointed out, there can be only two answers – either the sea levels have subsided, or the land has been raised. ‘The belief that all sedimentary rocks were deposited on the floor of a vast ocean that has since disappeared became known as the Neptunist theory, after the Roman god of the sea.’27 The alternative became known as Vulcanism, after the god of fire. By far the most influential Neptunist in the eighteenth century, in fact the most influential geologist of any kind, was Abraham Gottlob Werner, a teacher at the mining school in Freiburg, Germany, who proposed that, once one assumed that the earth, when it cooled, had an uneven surface, and that the waters retreated at a different rate in different areas, the formation of rocks could be explained. Primary rocks would be exposed first. Then, assuming the retreat of the waters was slow enough, there would be erosion of the primary rocks, which would drain into the great ocean, and then these sediments would be revealed as the waters retreated further, to create secondary rocks, a process that could be repeated and repeated. In such a way the different types of rock had been formed in a succession which comprised five stages. The first of them produced the ‘primitive’ rocks – granite, gneiss, porphyry – which had crystallised out of the original chemical solution during the Flood, and the last, which was not formed until all the flood waters had receded, was generated by volcanic activity – accounting for how lavas and tuff, for example, had been produced. According to Werner, volcanoes around the earth were caused by the ignition of coal deposits.28 He thought that volcanic activity had a trivial effect on the formation of the earth and though he was himself in no way interested in religion his Neptunist theory fitted very well with the biblical account of the Flood, which is one reason why it was so popular across Europe. It gave rise to the phrase ‘scriptural geology’.
This theory had tidiness to recommend it, but beyond that there were some serious problems. For a start, it did not even begin to explain why some types of rock that according to Werner were more recent than other types, were often found situated below them. Still more problematical was the sheer totality of water that would have been needed to hold all the land of the earth in solution. It would have to have been a flood many miles deep, and in turn that provoked an even bigger problem: what had happened to all that water when it had receded?
The chief rival to Werner, though nowhere near as influential to begin with, was a Scot, from the Edinburgh Enlightenment, James Hutton (1726–1797), and his Vulcanism. From the middle of the eighteenth century, some naturalists began to suspect that volcanic activity had produced some effect on the earth. It was noticed, for instance, that certain mountains in central France had the form of volcanoes though there was no record of such activity in history. Others pointed to the Giant’s Causeway in Ireland, which appeared to consist of columns of basalt that had solidified from a molten state and were therefore of volcanic origin. Hutton did not begin with the origins of the earth, but instead confined himself to observation rather than speculation. He looked around him at the geological changes he could see occurring in his own day and adopted the view that these processes had always been going on. In this way he observed that the crust of the earth, its outermost, most accessible layer, is formed by two types of rock, one of igneous origin (formed by heat), and the other of aqueous origin. He further observed that the main igneous rocks (granite, porphyry, basalt) usually lie beneath the aqueous ones, except where subterranean upheavals have thrust the igneous rocks upward. He also observed what anyone else could see, that weathering and erosion are even today laying down a fine silt of sandstone, limestone, clay and pebbles on the bed of the ocean near river estuaries. He then asked what could have transformed these silts into the solid rock that is everywhere about us. He concluded that it could only have been heat. Water was ruled out – an important breakthrough – because so many of these rocks are clearly insoluble. And so where did this heat come from? Hutton concluded that it came from inside the earth, and that it was expressed by volcanic action. This action, he realised, would explain the convoluted and angled strata which could be observed at many places all over the world. He pointed out that volcanic action was still occurring, that different landmasses were still rising and falling (there was evidence just then that areas of Scotland and Sweden were being raised), and that the rivers – again as anyone could see – were still carrying their silts to the sea.29