"If all this geological evidence of "deep time" speaks for itself, then why was there a need to come up first with the "principal" (apriori philosophy) of Uniformitarianism" - Hooberus
Uniformitarianism is, in essence, saying that the key to understanding past geological events comes from observing events taking place today (or in the 18-19th century when these principles were being developed). The assumption being that what is occurring now (then) has always occurred. Observations showed that sedimentary deposition takes place uniformly for a given location and extrapolating from that shows us that extremely thick beds of lithified sedimentary strata indicates vast periods of deposition. It was these observations that led early geologist to realise that the Earth was vastly older than the few thousands of years that had been accepted up until then. Geology has moved on since then but these principles are still valid, the difference now being we have many lines of evidence backing up these principles...
Perhaps if you understood these principles better you could answer your own questions?