An unconformity is a buried erosional surface or non-depositional surface, a contact between the rocks below and the layer of stratified rock above that is missing a significantly large interval of geologic time.
Lyell was a significant scientific presence through much of the time of Victorian England in the 1800s.
He had a large influence on the development and spread of the practice of geology as a science, partly through his textbook, that Charles Darwin read had a major influence in his thinking as he traveled around the world collecting samples, and Darwin consulted with Lyell at key stages during the time he developed and published his theory of evolution of species by natural selection.
Uniformtarianism does not require that all geological processes are slow.
Some are abrupt, such as an explosive volcanic eruption, an earthquake, or a landslide.
Geologists still use Steno's principles, with some refinements and additions.
They are summarized as the principles of relative geologic age determination, sometimes referred to as the principles of relative dating.
The combination of these two types of geologic ages makes a complete record of earth's geologic history in terms of the order of events and in terms of how many years ago each event occurred.
Relative geologic age refers to the order in which geologic events occurred.
In the early 1800s, soon after James Hutton died, William Smith in England made the scientific case for what came to be called the principle of faunal succession.
The key to this principle is that during a specific geologic time, only certain types of organisms existed, so if fossils of those organisms are found in a layer of rock, the rock is of that geologic age, the age when those organisms were species that lived on earth.
That means that tens of millions of years of geologic time lapsed between those two rock layers forming, and there is no sedimentary rock, no rock record, to record the details of what happened during that geologic time.