The Presence of the Namurian in the Bristol District

Abstract

The occurrence of massive reddish sandstones and quartzites lying between the Coal Measures and Carboniferous Limestone in the Bristol District has long been known. From their position and distinctive lithology, these beds have been referred to as the Millstone Grit by many early writers, amongst whom Austin (1865) may be mentioned. However, it has been shown that in part these beds are of Lower Carboniferous age. This was recognized by Vaughan (1905) notably in the Avon Section and at Long Ashton, where red grits and sandstones, previously regarded as Millstone Grit, were shown to represent horizon ∈, and later found by him to be of D3 age. Dr. Stanley Smith (1930) has shown at Wick, on the eastern border of the Bristol Coalfield, that the lower part of the red and gritty beds of that area are likewise of Avonian D3 age. Dr. Smith suggested a non-sequence between Lower and Upper Carboniferous to occur some 30 feet above a thin gritty limestone, the “Mollusca Band” of D3 age. Between this horizon and that from which Yorkian plants were recorded (Crookall in Smith, 1930, p. 342), some 350 to 400 feet of grits and micaceous shales occurred. These beds were of uncertain age, and Dr. Smith held the opinion that part and probably most of these beds belong to the Upper Carboniferous.