This spot on the earth’s surface which we now call Weymouth needed many million years to build and to mould into its present form.
During these long ages the district sometimes lay under the sea, and sometimes formed dry or marshy land. Its climate varied from sub-tropical to arctic, and its surface was subjected to alternate upheavals and depressions, and augmented by fresh deposits or denuded by weathering or erosion by streams or scouring by waves.
In those days and long before the advent of man, strange animals and plants inhabited the district and left their fossil remains for geologists to collect and investigate. The exhibits of this section introduce some of the more interesting of these ancient inhabitants and their environment. The chart below illustrates the evolution of life on earth from its very simplest forms with the ages in which the various lifeforms emerged.
The geology of the Weymouth area (Professor R Good’s “Weyland”) spans a rather narrower period, commencing about 130 million years ago and this period is defined in more detail in the next picture.
The next picture is a plan of “Weyland” showing the outcrops of the different geological formations of our neighbourhood. The age of the oldest of these – Fullers Earth – is about 130 million years, when reptiles as well as abundant fishes swam in the sea which then covered the area. Later the sea became gradually shallower, and by Purbeck & Wealden times the district had become a land surface oscillating about sea-level and consisting largely of brackish or fresh-water lakes.
Gradually the sea again encroached, and covered the Wealden land, and, about 90 million years ago, the deposit known as Lower Greensand was laid down, but the deposit did not actually reach quite as far west as Weymouth. Once again the crust rose, and the top of the Lower Greensand was planed off, and on the crust again subsiding, the Gault, Upper Greensand and Chalk were in turn laid down.
When the land again emerged a great thickness was denuded from the top of the Chalk before the lower Tertiary beds were deposited, and in the mid-Tertiary times, titanic uplifts and folding movements took place, which, in Europe, produced the Alpine ranges, and in our district folded the strata, breaking them across and displacing the sides of the fractures in “faults”, and sometimes pushing the broken blocks one over another in “thrusts”, so that here strata were carried down as much as 2,000 feet, while there they were bent up into arches, whose summits have subsequently been planed off by erosion.
This is illustrated in the picture below that shows a section through the area designated by the line ‘AB’ in the plan above.
These images are taken from information boards once displayed in Weymouth Museum.