Moor Mill Quarry, West

Site of Special Scientific Interest · 51.7119, -0.3506

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Also within

Hertfordshire County

Condition (Natural England)

Unfavourable No Change (1)
UnitFeatureConditionArea (ha)Assessed
TL140027 — Unfavourable No Change 0.17 2009-02-13

Habitats

Fast flowing river and stream

Geology & landscape

Geological Period: Quaternary · Rock Type: Chalk, Glacial Till

Landscape processes: Fluvial, Glacial

Description

Description The pit shows a complex sequence of Pleistocene Pre Anglian Anglian deposits overlying the chalk. The lowest of these is fluvial gravel of Thames origin, above which are lacustrine laminated silts, in turn being overlain by chalky glacial till. Above the till is a second gravel, differing from the first in that it was deposited by a westerly flowing river, probably the Colne. This sequence has been interpreted as representing the blocking of the pre Anglian Thames Valley by ice, resulting in the formation of a lake, which was later overrun by a further advance of ice, culminating in the diversion of the Thames into its modern valley and the initiation of Colne drainage in the area. This is the only siteat which this sequence can be demonstrated and as such is of fundamental importance in tracing the diversion of the River Thames from its pre Anglian course.

Plant communities

A9 — Fast flowing river and stream, Marginal and inundation, Pond ditch and canal, Sluggish river and stream

Potamogeton natans community

Schoenoplectus lacustris, Juncus bulbosus, Sparganium angustifolium, Sparganium erectum, Sparganium minimum, Alisma plantago-aquatica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Elodea canadensis, Lemna minor, Lemna trisulca, Nymphaea alba, Callitriche platycarpa, Callitriche stagnalis, Littorella uniflora, Potamogeton natans, Ranunculus trichophyllus, Glyceria fluitans, Chara subspinosa

A14 — Fast flowing river and stream

Myriophyllum alterniflorum community

Isolepis fluitans, Juncus bulbosus, Fontinalis antipyretica, Lobelia dortmanna, Equisetum fluviatile, Myriophyllum alterniflorum, Lemna minor, Callitriche stagnalis, Littorella uniflora, Potamogeton filiformis, Potamogeton gramineus, Potamogeton natans, Ranunculus peltatus, Chara spp., Nitella hyalina

A17 — Chalk river and stream, Fast flowing river and stream

Ranunculus penicillatus ssp. pseudofluitans community

Berula erecta, Nasturtium officinale, Elodea canadensis, Lemna minor, Callitriche stagnalis, Veronica beccabunga, Polygonum amphibium, Polygonum hydropiper, Potamogeton crispus, Potamogeton pectinatus, Ranunculus penicillatus ssp. pseudofluitans

A18 — Fast flowing river and stream

Ranunculus fluitans community

Fontinalis antipyretica, Fontinalis squamosa var. curnowii, Myriophyllum alterniflorum, Myriophyllum spicatum, Elodea canadensis, Mentha aquatica, Lemna gibba, Lemna minor, Potamogeton perfoliatus, Ranunculus fluitans, Glyceria fluitans, Phalaris arundinacea