DIFFORMITATEM EarthCache

‘No vestige of a beginning – no prospect of an end’ However, in his own words:

I was surprised with the appearance of vertical strata in the bed of the river, where I was certain that the banks were composed of horizontal strata. I was soon satisfied with regard to this phenomenon, and rejoiced at my good fortune in stumbling upon an object so interesting to the natural history of the earth, and which I had been long looking for in vain.

… above those vertical strata, are placed the horizontal beds, which extend along the whole country.

(Hutton, [1795] 1959, vol. 1, p. 432,

What Hutton had found was what is now known as an ‘unconformity’: a junction between sets of rocks of quite different types, formed at quite different epochs.

An angular unconformity forms when rock deposited in horizontal layers is folded or tilted and then eroded.
When erosion stops, a new horizontal layer is deposited on top of the tilted layer.
When the bedding planes of the older rock layers are not parallel to those of the younger rock layers deposited above them, an angular unconformity results.

Sometimes, layers of sediments are uplifted without folding or tilting and are eroded. Eventually, the area subsides and deposition resumes.
The layers on either side of the boundary are nearly horizontal. Although the rock layers look as if they were deposited continuously, large time gap exists where the upper and lower layers meet.
This gap is known as a disconformity.