On the off-chance that you are on the lookout for a geological fault-line in your garden, here is the sort of thing you should be looking for:
Here, the Howgill Fells have been squashed up against the younger, limestone rocks of the Yorkshire Dales, sliding over the top of them, thereby creating the Dent Fault.
If you do happen to notice one of these in your garden, please let me know.
The Dent Fault was discovered by local lad, Adam Sedgwick, who went on to teach Charles Darwin geology at Cambridge University. He was a great geologist, but could never bring himself to accept his famous pupil's theory of evolution by means of Natural Selection.