- GeoRef, Copyright 2004, American Geological Institute. Reference includes data from Bibliography and Index of Geology Exclusive of North America, Geological Society of America, Boulder, CO, United States
The stratigraphic column of Carboniferous rocks in southwest England is reviewed, and five new groups are proposed to be equivalent to the lower, middle, and upper Culm divisions established by Ussher in 1901. It is shown that the youngest of these, the Ugbrooke group, shows no cleavage and is separated by a major unconformity from the underlying Devonian and Carboniferous rocks with well-developed slaty cleavage. The major orogeny of the region is therefore pre-Ugbrooke in age. In the discussion, the idea of a major unconformity within the Carboniferous in the area is questioned, and it is pointed out that the presence or absence of cleavage is unreliable for dating strata. Subsequent discussion presents the author's agreement with the first item, but holds that the subject of cleavage remains to be investigated.