By Jason Curtis Droboth
January 20, 2020
A short paper for GLGY 699: Philosophy of Geoscience
James Hutton was searching for a way to explain why, if erosion is a consistent destructive force, there is still solid material above the ocean. To answer this, he conjectured that new rock must be added to the terrain to offset the destructive nature of erosion (Hutton, 2018). His mechanism for this? Heat.
The inductivist approach to generating scientific knowledge reasons that through a “finite set of observations, one can infer something about a potentially infinite set” and thus determine, from observations of the specific, more general truths (Gimbel, 2011). Hutton used a set of key finite observations to argue or formulate his more general grand theory known as Plutonism. He observed that:
1. Rocks are eroded by water and carried to the ocean (Hutton, 2018).
2. Volcanoes exhume hot lava which becomes new rocks (Hutton, 2018).
3. Terranean rocks are composed of bits of material similar to the loose material found on ocean beaches (Hutton, 2018).
4. These rocks occur at high alpine elevations (Hutton, 2018).
5. Strata are often tilted, folded, overturned, and crosscut as seen at outcrops like that at Siccar Point (Hutton, 2018, Repcheck, 2009).
6. Veins or masses of foreign rock cut through other rocks like that seen at Glen Tilt (Hutton, 2018, Repcheck, 2009).
7. Granites lay at the heart of most mountains (Hutton, 2018).
In a general sense, Hutton used these observations in an inductive method to propose a new mechanism to explain these phenomena. He, along with others at the time, observed that the process of erosion slowly erased rocks and carried their weathered particles to the sea (Gimbel, 2011). It was also known that new rock could form as a result of heat, a process clearly observed during episodes of eruptive volcanism (Gimbel, 2011). But explaining the remaining observations was challenging.
The problem Hutton was attempting to solve only existed as a result of three general assumption. First, a uniformitarian view of history (Hutton, 2018). Second, that the Earth is old (Hutton, 2018). Third, that the rocks under consideration could not be formed by precipitation out of water (Hutton, 2018). Removing any one of these assumptions could sufficiently remove the problem. But he held on these assumptions and thus required a mechanism or mechanisms to explain why vast mountains and terrestrial rocks had not fully vanished into the sea after years of relentless erosion.
To Hutton, it was clear that new rocks had to replace the rocks removed by erosion over Earth’s long history. Subterranean heat is what leads to the 2 necessary events: the formation of new rocks by fusing sediment together and its uplift well above sea level by great thermal expansion (Hutton, 2018). The idea of plutonism not only explained how rocks formed but why they occur at such high elevations above sea level and in such complex arrangements.
While John Stewart Mill appreciated Isaac Newton’s method of induction through universal generalizations, he thought it was still not a diverse enough tool. Instead, he proposed 4 methods of experimental inquiry (Gimbel, 2011). Mill saw each of these methods as a different inductive tool to be used in different circumstances. To employ the method of agreement, one can infer the cause of an event if all causes and events except one change (Gimbel, 2011). The one cause and the one event that did not change, can be linked. The method of differences is similar, except that by removing only one cause of many, the one effect that disappears can be linked to the one removed cause (Gimbel, 2011). By increasing or decreasing the frequency or magnitude of a cause and observing a proportional change in the event, one can link that cause and event though the method of concomitant variations (Gimbel, 2011). Finally, the method of residues suggests that if the causes of each event except one are known, the remaining cause must by default be linked with the remaining event (Gimbel, 2011).
By applying the aforementioned assumptions as the lenses through which to systematically and logically interpret his 7 main observations, Hutton inferred through Mill’s methods the 2 main events and the 1 primary mechanism that explain the nature of the observed phenomenon. The process of thought may have occurred like this.
1. As was directly observable in Hutton’s time, terrestrial material is eroded and transported by water to oceanic coastlines and ocean bottoms (Hutton, 2018). The nature and magnitude of this process observed in Hutton’s time, remained constant throughout all of Earth’s past and vast quantities of material must have been deposited in the ocean, layer upon layer (Hutton, 2018).
2. Some rocks are formed when molten rock breaches the Earth’s surface during volcanic explosions (Hutton, 2018). Thus, rock can be formed with heat and there must be a subterranean source of heat.
3. Much rock, displaying distinct strata, appeared to be composed of similar material to that found on beaches, such as sand and shells (Hutton, 2018). These rocks must have been formed in direct interaction with oceans. Sediment at the bottom of the ocean is buried and heated up enough to fuse it into new stratified rock (Hutton, 2018).
4. The same subterranean heat responsible for the violent expansive forces associated with volcanic activity lifts these new rocks well above sea level to alpine elevations (Hutton, 2018).
5. During this uplift, strata originally deposited and fused horizontally according to Steno’s principle of horizontality are then fractured, tilted, folded, and overturned (Hutton, 2018),2.
6. These same expansive forces can push melted rock up from below, penetrating existing rock bodies to form cross-cutting veins or masses of rocks or crystals foreign to that of the surrounding bodies (Hutton, 2018). The method of concomitant variations would suggest that subterranean heat is the main cause of these veins since they tend to occur more in areas of higher volcanic activity and less in areas of lower volcanic activity.
7. Since new rocks form at great depths, the masses of granites at the heart of most mountains formed from below, pushing into overlying rocks (Hutton, 2018).
One might assume that Hutton intentionally employed a method of systematic induction from empirically observed evidence. However, the truth is more convoluted.
Uniformitarianism is somewhere between an idea and an observation, employing a complex combination of both deductive and inductive reasoning. It’s based on real observations of Earth’s natural state and natural processes, primarily erosion. However, those natural processes observed in Hutton’s time, were assumed to be equally as influential in the past (Gimbel, 2011). Hutton’s assumption that the Earth is old is also a product of his uniformitarian worldview. The complex stratigraphic structures like those he observed at Siccar Point must have taken immense amounts of time to form since the observed rate at which the cycle of weathering, erosion, transportation to the sea, crystallization, and uplift occurred was very slow (Repcheck, 2009). The assumption of an old uniformitarian Earth allotted the necessary time to form the complex features he observed (Gimbel, 2011). While he did employ inductive logic by using observations of the specific (cross-cut beds) to infer the general (Earth is old), he also employed somewhat of a deductive logic by starting with a primary premise because he needed it to be true (Earth is old), stating a secondary premise (Earth’s surface gets more altered over time), and deriving a more specific conclusion (Earth’s surface is highly altered).
Today, Hutton’s idea of Plutonism, or at least its emphasis on the important expansive forces and rock-forming ability of subterranean heat are still accepted as one of the key mechanisms used to explain modern observations. Far ahead of his time, it might seem to some that he had an uncanny ability, similar to that of Isaac Newton, to infer general and universal causes from finite and specific observations. But history tells a much more complex story.
Hutton, J. Abstract of a Dissertation Read in the Royal Society of Edinburgh, Upon the Seventh of March, and Fourth of April, M, DCC, LXXXV, Concerning the System of the Earth, Its Duration, and Stability. (GALE ECCO, PRINT EDITIONS, 2018).
Gimbel, S. Exploring the scientific method : cases and questions. (The University of Chicago Press, 2011).
Repcheck, J. The man who found time : James Hutton and the discovery of the Earth’s antiquity. (Basic Books, 2009).