E. Cobham Brewer 18101897. Dictionary of Phrase and Fable. 1898.
Mam Tor, a hill on the Peak of Derbyshire; so called from the waste of its mass by shiveringthat is, breaking away in shivers or small pieces. This shivering has been going on for ages, as the hill consists of alternate layers of shale and gritstone. The former, being soft, is easily reduced to powder, and, as it crumbles away, small shivers of the gritstone break away from want of support.