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by a normal projection onto it of the individuals representing a
species form that occur within that unit sample'. Cover
estimates are usually obtained using a modifi cation of the point
quadrat method used in ecology. Typically a clear plastic sheet
marked with 100 randomly distributed points is overlain on an
exposed bedding surface (Figure 5.14) and the number of 'hits'
of these points on various taxa are scored and expressed as
percentage cover. It follows from this that a single bedding
surface must be completely exposed over the sample area.
Foreshores and some quarry fl oors provide the opportunities.
However, in practice this is very diffi cult and some workers
prefer to exhume blocks of matrix, each with a plant-bearing
face exposed, and arrange these to form a sample area from
which cover estimates are taken. The gaps between the blocks
are scored as 'space'. Extra random points are then scored until
the total score for plant material plus bare rock reaches 100.
5
taxon A
taxon B
taxon C
taxon D
taxon E
taxon F
(
(
Figure 5.14 (a) Line drawing of Jurassic plant fossils from Cayton Bay, Yorkshire, UK, made from an exposed
bedding plane with an overlain 0.5 m × 0.5 m point quadrat shown in (b). For purposes of visualization the 100
randomly distributed points have been expanded into yellow circles.
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