I think maybe your right?
In Ffestiniog it is of cource a steeply inclined cleavage, but in Cumbria it tends to be more or less vertical, though this can vary.
At Honister the agle is about 30 degrees, at Burington about 70 degrees.
Since cumbrian slate tends to be much harder, bacaue of it's volcanic origin, it is sometimes difficult to tell what is bedding and cleavage & other.
Lets also note that these workings tended to be quite early, and driving levels into the hillside was almost un-heard of.
Kein geneis kanaf - Cain gnais canaf
Byt vndyd mwyhaf - byth onddyth moyav
Lliaws a bwyllaf - Líows o boylav
Ac a bryderaf - ac o boryddarav
Kyfarchaf y veird byt - covarcav yr vairth
Pryt nam dyweid - poryth na'm dowaith
Py gynheil y byt - Pa gonail y byth
Na syrch yn eissywyt - na soroc yn eishoyth
Neur byt bei syrchei - nour byth bai sorochai