Irene Preston's Historical Writing
GEOLOGY OF CHESHIRE
Approximately 250 million years ago during a period known as
the Permian/Triassic, a large land mass moved across the
equator. Desert conditions prevailed as in the present-day
Sahara with a sea to the east called the Zechstein.
Parts of the land were low-lying and were flooded regularly by
the Zechstein Sea leaving layers of salt. Over millions of years
these salt layers sank and were eventually buried and covered
with more sand. As these layers reached great depths the heat
and pressure changed the sand into sandstone and crystallised
the salt into halite. The vast land mass was situated between 15
and 20 degrees north of the equator.
This area is known as the Cheshire Basin and has been the
source of salt for over 2 thousand years.
Prior to the Permian period we have the Carboniferous period
covering three phases of sedimentary deposition which took
place some 354 to 290 million years ago.
The moving plates brought various land masses together south
of the Equator. This produced corals and many shell-like
creatures over millions of years and as they died they gradually
built up layers of lime sediment which became limestone due to
internal heat and pressure. Derbyshire and the Peak District are
well known for limestone and fossils.
Another large land mass in the north had a vast mountain range
which began to erode as it collided with the southern land mass
and gave us the grits, clays and pebbles. Huge deltas were
formed which were eventually seeded by ancient tree ferns
growing to great heights. These deltas would be similar to the
swamps around the coast of Florida where tidal waters invade
the area and cover the roots and fallen trees.
It is this process which eventually produces a black sediment and after
becoming buried like the lime sediment the carbon in the vegetation
becomes what we call coal.