Either of these events would have produced an unconformity; the two make it more pronounced.

They are separable into a lower and upper division with an unconformity often occurring between them.

At Llandovery they rest unconformably upon Ordovician rocks (Bala), but in many other places no unconformity is traceable.

An unconformity thus records movements of the crust and a consequent break in the deposition of the strata.

Such an erosion surface, called an “unconformity,” marks a gap in the geological record of the district where it occurs.

An unconformity may indicate that the beds below it have at some time been raised above the sea and have been eroded.

If beds of rock may be regarded as leaves in the volume of geologic history, an unconformity marks a gap in the record.

And if the unconformity be widespread, the lost interval is correspondingly great.