Chatsworth Grit
(25 to 60 m thick)
This is called the Huddersfield White Rock in the north of our region and was also formerly known as Rivelin Grit near to Sheffield. The Chatsworth Grit is the "millstone grit" of school textbooks, since it was extensively quarried for the manufacture of grinding stones for corn and paper mills, drinking troughs and architectural stonework (Fig. 4).
It consists of fine- to coarse-grained, massive and cross-bedded sandstones, with minor interbedded mudstones and siltstones. Pebbly layers are frequent and casts of large fragments of drifted trees are not uncommon (Fig. 5).
The Chatsworth Grit represents the culmination of an upwardly coarsening, prograding succession, i.e. it is a delta-top deposit. Palaeocurrent directions mostly suggest a consistent flow of braided rivers, flowing towards the south-west or west (Fig.6).
Recent studies have identified a major incised palaeochannel of regional significance in this unit (Waters et al, 2008).
Ashover Grit
(up to 27 m thick)
The Ashover Grit becomes more important to the south of our area, but is only known from boreholes within its boundaries.