Brigg Matters Issue 68 Spring 2023

Brigg Geology Group
The group’s pre-Christmas social
and quiz night raised £24 from the
proceeds of a raffle, the prizes for
which had been kindly donated
by several of those attending. A
cheque for the amount raised was
presented to the Brigg Servicemen’s
Club on 27 th January in recognition
of their continuing support.
At the January meeting, Moira
Smith, a recent regular attendee at
meetings, brought in a collection
of rocks, minerals and fossils some
from her Kings Avenue garden.
Amongst them were a couple of
specimens that I would like to
feature, the first a block of the
mineral fluorspar (or fluorite)
shaped to form an attractive
paperweight. This is a variety known
as ‘blue john’ which has bands of
blue and yellow and which give it its
name as it is an anglicised version
of the French bleu and jaune. It was
highly prized by the Romans when
they discovered deposits in the
caves of Derbyshire.
The second specimen that caught
my attention was a sea urchin
(echinoid) fossil, the only members
of the Animal Kingdom with 5-fold
symmetry (A), which is so well
preserved in flint that it can be
identified to its species, Echinocorys
scutata. Echinoids of this type are
identified by the relative position
of the mouth and anus (B) as well
as general body shape. This species
is typical of the Chalk and ranges in
age from 92 to 66 million years ago
(Late Cretaceous). I have found this
species in quarries at Ulceby, Great
Limber and Barrow-on-Humber.
The test (shell) of this sea urchin is
covered in post mortem scars caused
by marine worms which have found
it a useful foundation on which to
secrete their tubular housing.
By its state of wear, Moira’s
specimen was almost certainly
collected from gravels that were
the product of the wearing away
by Paul Hildreth
Shaped block of ‘Blue John’ fluorite showing
yellow (y) and purple-blue (b) veining
(Scale bar = 5.5cm)
Posterior view of echinoid showing its general
shape and symmetry.
(Scale bar = 4cm, wt = worm tube scar)
Oral view of echinoid showing the relative
positions of the mouth (m) and anus (a).
(Scale bar = 2cm, wt = worm tube scar)
of the Chalk by ice and their later
deposition by meltwater. The
deposits at Kettleby are an example
of such chalk-flint gravels.
The Yorkshire Geological Society
is holding its annual ‘open day’
on Saturday 29th April at the
National Coal Mining Museum
(NCMME) between Wakefield
and Huddersfield. There will be
guided tours, both surface and
underground, displays, hands-on
activities and a chance to have
specimens identified by experts or
even cut to reveal what lies within.
The afternoon will also include short
talks on a variety of geological topics
including fish poo, fatally-bitten
ammonites and how to extract tiny
fossils from rocks using a pair of
tights! Activities are free and aimed
particularly at youngsters and family
groups. There are catering facilities
within the museum and ample car
parking. Two of us, Mike Oates
and myself will be participating,
Mike with a demonstration of fossil
cleaning and preparation and I shall
be taking my Flamborough Head
display together with a collection
of fossil sponges (the subject of my
January talk).
Programme:
Thursday 23 rd March: “Geology in
Brigg” – an illustrated talk on the
rocks and fossils to be found in the
town’s buildings, footpaths and
monuments. Brigg Servicemen’s
Club, 7.45pm.
Thursday 27 th April: “British
Mesozoic fossils and the emergence
of mammal traits” by Dr. Elsa
Panciroli. A highly recommended
ZOOM webinar on the early
evolution of mammals organised by
the Yorkshire Geological Society (I
shall be on duty handling the Q&A
session). Book a place by using the
website (www.yorksgeolsoc.org/
events) and click on the page to bring
up the registration button.
38 Brigg Matters
Brigg Matters 39