Home News Project info River Wye Links geology Beneath almost the whole of the study area the rock is the Old Red Sandstone, which gives the characteristic colour to the local soil. These rocks originated in the Devonian Period (354-417 million years ago) as sediment laid down by rivers meandering across a broad flat tropical coastal plain. This material was the product of the gradual erosion of older rocks. Although many millions of years of sedimentation formed newer strata of rocks above the sandstone, including those formed in the Cretaceous period by the great Chalk Sea which once covered England, all of these have subsequently been eroded away. The Cretaceous period was the last one in the Mesozoic (middle life) era. The very oldest rocks were formed in the Pre-Cambrian. This is the supereon of geological time from the formation of the earth, around 4,500 million years ago, to the evolution of hard-shelled animals in the early Phanerozoic (meaning ‘revealed life’) some 545 million years ago and covers 88% of the earth’s history. Pre-Cambrian strata are buried beneath more recent layers of sedimentary rocks and are often referred to as ‘basement’. Here and there, these ancient rocks are visible on the surface, such as the outcropping Pre-Cambrian rocks of the Malvern Hills on the eastern edge of Herefordshire. Most of the named divisions of geological time are named from the fossils found within the rocks of the Cambrian period. There was a growth in the number of fossils representing the sudden appearance of many groups of animals. The Cambrian was the earliest bit of the Phanerozoic eon. The name Phanerozoic derives from Greek and means visible life. It is the eon in which we live and has lasted for about 545 million years. The Phanerozoic eon is sub-divided into the Palaeozoic, Mesozoic and Cenozoic eras.   Phanerozoic eon Palaeozoic era Mesozoic era Cenozoic era The Palaeozoic Palaeozoic means 'old animals', and is named from the fossils of ancient animals founds within its rocks. The earliest rocks in the series were first identified in Wales and so the ancient name for Wales - Cambria - is used for them. The Cambrian was followed by the Ordovician (named for the Ancient British tribe of central Wales) which saw the replacement of many of the life-forms of the Cambrian with newer ones. This seems to have followed a major extinction event - the Cambrian-Ordovician extinction   Palaeozoic Cambrian Ordovician Silurian Devonian Carboniferous Permian 545m - 488m 488m - 443m 443m - 416m 416m - 359m 359m - 299m 299m - 251m Another Ancient British tribe, the Silures of south Wales, gives the name Silurian to the third division of the Palaeozoic. It was during the Silurian that life, in the form of mosses, colonised the land. The Herefordshire Lagerstätte - it is from the Silurian period that some of the most interesting fossils found in Herefordshire come and they are international importance. This group of invertebrate animals were living on the bed of the ocean 425 million years ago when they were killed and buried, and finally preserved by, a sudden fall of volcanic ash. One of these small animals was a previously unknown arthropod, which was given the name Cinerocaris magnifica. Another previously unknown species was Acaenoplax hayae, known to the discoverers as 'the spiny worm'. Acaenoplax is a type of mollusc, therefore in the same phylum as squids, slugs and snails. There was also a species of Bdellacoma, a genus of starfish and early barnacles. The area that these fossils were found in is one of the few parts of the county where the later Devonian rocks have not buried the Silurian formations. The image below is of a fossil of a creature which inhabited Herefordshire before the Old Red Sandstone was formed. This is the small (the shell is a few  mm long) ostracode crustacean Nymphatelina gravida Siveter et al, 2007. 'One half of the bivalved carapace has been removed to show the internal morphology.  The 'yellow', isolated spheres and boat-shaped objects in the posterior part of the shell are interpreted as eggs and possible juveniles within the carapace, thus demonstrating a remarkably conserved egg brooding reproductive strategy within these ostracodes over 425 million years.  The other coloured parts of the morphology pick out, for example, the  various appendages and the gills.' Derek Siveter image © Siveter et al, 2007 One of these areas is the Woolhope Dome, a geological anticline where rocks of the older, Silurian period, form an island within the Old Red Sandstones of the Devonian. At Hough Woods the oldest rocks of the Silurian come to the surface, these are the rocks of the Llandovery series and were deposited world-wide 444 to 428 million years ago. In decreasing age the rocks surrounding this formation are the Woolhope, Much Wenlock and Aymestrey limestones which form the concentric scarps of the 'dome'. The fourth period of the Palaeozoic, the Devonian, takes its name from the county of Devon, where rocks of this period were first studied on Exmoor. This is the period of the old red sandstone, the rock of Herefordshire which was laid above the Silurian rocks in our area. The red colour of the Old Red Sandstone is due to the presence of oxygen during the creation of these rocks - these sandstone layers have been described as the 'rust of the earth'. Although many millions of years of sedimentation formed newer strata of rocks above the sandstone, including those of the great Chalk Sea, which once covered England, all of these have subsequently been eroded away. The newest Old Red Sandstone rocks in the area, covering the parishes of Hentland, Sellack, Bridstow, Brampton Abbotts, Kings Caple and Foy, are those of the Brownstone Formation. The older St Maughans foundation forms the surface rock beneath the parishes of Ballingham, Bolstone and Holme Lacy. Natural exposure of rock of the Brownstones formation of the Old Red Sandstone near Ross-on-Wye     Exposure of rocks of the Brownstones formation in an old quarry at Bridstow     Closer view of the above     St Maughans formation rocks exposed in an estate quarry by the River Wye on the north side of Brockhampton parish     Natural exposure of St Maughans formation sandstones at Holme Lacy where the river is still eroding them.     This erosion leads to landslips of the sort that form the bank on the right here here. (Immediately upstream of the previous view and from the opposite direction). The gravels of the river bed on the the left are now abandoned unless the river is in flood.     Just downstream of Red Cliff is this abandoned river-bank.     The present floodplain of the Wye looking left from the previous view.     The fifth period of the Palaeozoic, is the Carboniferous. Generally rocks of this period are absent from Herefordshire – less than 1% of Herefordshire’s surface area is carboniferous rock – but in the Symonds Yat area, Devonian Old Red Sandstone is overlain with strata of the Carboniferous Limestone Series. Caves in the Symonds Yat rocks would provide some of the earliest human shelters found in Herefordshire.  The final period in the Palaeozoic is the Permian, which ended with the greatest extinction of species known. This was the Permian-Triassic extinction event in which over 90% of marine species and perhaps 70% of land species died out. Permian rock formations are absent from Herefordshire but outcrops in Worcestershire as the geological strata of England slopes downwards from west to east. The era which followed the Palaeozoic is the Mesozoic, meaning 'middle animals', and the era is sometimes known as the 'Age of the Dinosaurs'. At the beginning of the Mesozoic almost all the land on earth formed a single continent, known to geologists as Pangaea which gradually split up, so that by the end of the era, the continents that we now know were formed. Rocks of the Mesozoic’s three periods of Triassic, Jurassic and Cretaceous are, like those of the Permian, absent from the study area.  Mesozoic era Triassic Jurassic Cretaceous 251m - 199m 199.6m  - 145.5m 145.5m  - 65.5m   During the final, and longest, period of the Mesozoic, the Cretaceous, chalk deposits built up over most of England. In the west, including the study area, these have long since eroded away, but they surface in the south-east and characterise England’s coastline at Dover, Beachy Head and the Isle of White. It is in the chalk that flint, the favourite raw material of prehistoric tool-makers occurs. The Cretaceous ended 65 million years ago. It would be over 64 million years before humans arrived in Britain. During this time the earth underwent period of warming and cooling – one warming period was extremely rapid and led, at the Paleocene-Eocene Thermal Maximum, to the Polar Regions being entirely ice-free. Mammals spread and diversified to fill the ecological niches previously occupied by now-extinct species of dinosaurs.  These last 65 million years form the Cenozoic – 'new life' – era, which is the era in which we live. It is divided into two periods, the Palaeogene and the Neogene. These, in turn, are sub-divided into epochs. The Palaeocene, the Eocene, Oligocene epochs form the Palaeogene while the Neogene is divided into the Miocene, the Pliocene, the Pleistocene and the Holocene. the Palaeogene It was in the Palaeocene, the first epoch of the Palaeogene, that mammals, taking advantage of the mass extinction of the dinosaurs diversified to take advantage of then-vacant ecological niches. There were four branches - monotremes, marsupials, placental mammals and multituberculates Globally, the climate appears to have been quite warm and tropical, sub-tropical and deciduous forest appeared. At the end of the epoch the planet saw its extreme global warming event and even the polar regions were free of ice. Marking the the second epoch, the Eocene, Earth saw one of the most rapid  and extreme warming events known to geologic history. This is called the Paleocene-Eocene Thermal Maximum or Initial Eocene Thermal Maximum. During the Eocene, India began to collide with Asia and consequently created the the Himalayas. It is within a fairly short period of the early Eocene that the earliest known fossils of most orders of mammals which still exist today are found. The Oligocene is the third and last epoch of the Palaeogene. Many grasses appeared during this epoch as did early horses.   Cenozoic era Palaeogene Neogene Palaeocene Eocene Oligocene Miocene  Pliocene Pleistocene Holocene 65m - 56m 56m - 34m 34m - 23m 23m - 5.33m 5.33m - 1.8m 1.8m -11,550 11,550 - present the Neogene The Miocene was the first epoch of the Neogene. Warmer than those in the preceding Oligocene or the following Pliocene, it saw the expansion of grasslands and the creation of kelp forests. The second Neogene epoch, the Pliocene, saw global cooling and the enormous spread of grasslands encouraging the proliferation of grazing mammals. Ice began to accumulate at the poles. This would lead to the ice ages. It is only in the third and fourth epochs of the Neogene, the Pleistocene and the Holocene that humans began to inhabit the Herefordshire landscape.     Back to TOP

Wye Valley Archaeology pages

maintained by Archenfield Archaeology Ltd