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The Grey Chalk Subgroup (formerly the Lower Chalk minus the Plenus Marls) is usually relatively soft and greyish in colour. It is also the most fossiliferous (especially for ammonite fossils). The strata of this subgroup usually begin with the ' Glauconitic Marl Member' (formerly known as the Glauconitic or Chloritic Marl), named after the ...
The Chalk Group which includes all of the different units which make up the succession in England, is subdivided into an earlier/lower Grey Chalk Subgroup and a later/higher White Chalk Subgroup. The Chalk has previously been subdivided in other ways and references to Upper, Middle and Lower abound in the literature and on geological maps.
The Ulster White Limestone Group is a late Cretaceous lithostratigraphic group (a sequence of rock strata) in Northern Ireland. The name is derived from the characteristic chalk rock which occurs particularly along the Antrim coast.
It rests in some places on the Red Crag Formation and in others unconformably on Coralline Crag, Palaeogene formations and Chalk Group bedrock. It is overlain by the Wroxham Crag Formation, and unconformably by the Kesgrave Catchment Subgroup (part of the Dunwich Group) and Mid Pleistocene glacigenic deposits.
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Subgroup analysis refers to repeating the analysis of a study within subgroups of subjects defined by a subgrouping variable. For example: smoking status defining two subgroups: smokers and non-smokers.
Chalk is a soft, white, porous, sedimentary carbonate rock.It is a form of limestone composed of the mineral calcite and originally formed deep under the sea by the compression of microscopic plankton that had settled to the sea floor.
An interesting example is the modular group = (): it acts on the tree given by the 1-skeleton of the associated tessellation of the hyperbolic plane and it has a finite index free subgroup (on two generators) of index 6 (for example the set of matrices in which reduce to the identity modulo 2 is such a group).