[thackney]

I’m not a big wiki fan, but they give a simple summary.

Portland Group (geology)
http://en.wikipedia.org/wiki/Portland_Group_%28geology%29#cite_note-1

The Portland Group (or Portlandian) is an Upper Jurassic lithostratigraphic group (a sequence of rock strata) in south-east England.

The rocks include limestones, dolomitic sandstone, siltstone and mudstone. It is divided into two formations; the Portland Stone Formation (or ‘Portland Limestone Formation’) and the underlying Portland Sandstone Formation (or ‘Portland Sand Formation’). The Portland Stone Formation is further divided into a lower Portland Chert Member and an upper Portland Freestone Member, both of which are limestones. The Portland Sand Formation is made up largely of dolomites but includes siltstones and fine-grained sandstones in its lower parts.

[Red Badger]

LOL! I thought they found a new reservoir of cement materials!................