Geoscience Reference
In-Depth Information
Richardson examined the ground for himself, and published a number
of papers between 1802 and 1812. He was clearly upset at others
discussing the geology of an area which they had visited briefly or
not at all. He believed he had the authority, as a long-term resident,
to make his views known. While he claimed not to subscribe to any
theory or belong to any faction, he held (perhaps unwittingly) to the
Neptunist theory for the origin of the basalt. He rejected the alterna-
tive theories on a number of grounds:
1. There was no evidence of a volcanic mountain or cone in Antrim;
2. Plants are found developed on lava flows but not in between the basalt
layers;
3. The constituents of basalt and lava were different;
4. The layers of basalt were horizontal and regular in thickness;
5. The physical appearance of basalt and lava were different;
6. The contact relationships of basalt and lava were different;
7. The basalt was divided into regular masses while lava is found as a
irregular mass;
8. The dykes of Antrim were different from those seen in Scotland by
Hutton;
9. The basalt of Portrush contained fossil marine shells.
The ammonite-bearing basalt was discovered by Richardson in about
1799 and was proof to him and to Kirwan that this lithology was
deposited in water. Specimens were sent to Trinity College Dublin,
to Kirwan and other geologists, and to Edinburgh in 1801, where they
were examined by Sir James Hall, Lord Webb Seymour and John
Playfair who recognised their sedimentary nature. The rock is now
known to be Lower Jurassic Lias mudstone, which contains specimens
of the ammonite Paltechioceras. The Edinburgh scientists noted that
the Portrush rock had been baked by hot basaltic material (actually
dolerite of what is now termed the Portrush Sill) close by, and this was
what had made its appearance so similar to that of basalt. On visiting
Edinburgh, Richardson was brought to see Arthur's Seat where Playfair
tried to persuade him of his error. Richardson held firm in his beliefs.
