Evaporites are non-clastic, or chemical sediments, created through the precipitation of dissolved salts from water. They most frequently occur at the site of a former large water body such as a lake or landlocked sea, on coastal plains (sabkha zones), or where rivers feed very arid desert areas. As the water involved slowly evaporates the salts become more concentrated and at well-defined concentrations they begin to recrystallise. They are different to the more conventional clastic sedimentary rocks which include mudstone, siltstone and sandstone.

Sometimes referred to as salines, these rocks form an economically important group of minerals. Sylvite (potassium sulphate) and minor amounts of halite (rock salt) are extracted by Cleveland Potash Ltd. from their mine at Boulby, near Staithes. This is Europe’s deepest shaft mine as the sylvite lies within Permian strata over a kilometer below the surface. They are some 290 million years old and were laid down when a shallow ancient sea, dubbed the Zechstein and which occupied much of northern England, underwent several cycles of evaporation and transgression. Sea water comprises ~3.5% dissolved salts of which the bulk is sodium chloride or common salt. Evaporation yields successively limestone, anhydrite (calcium sulphate), halite and finally potassium and magnesium salts. Anhydrite was formerly mined and processed at Billingham on Teesside.

Evaporite deposits can flow under pressure producing salt-domes which disturb the strata through which the pass and internally exhibit complex folding. They also retain heat and may be a target for future geothermal energy projects.

Images above show:
Sylvite – as mined at Cleveland Potash Mine, Boulby, Cleveland.
Halite – also found within Boulby Mine.
Cleveland Potash Mine, Boulby, East Cleveland. UK.
Anhydrite – once mined at Billingham on Teesside.

This mineral is able to assume almost any colour but commonly brown, yellowish-brown, or grey specimens can be found. It occurs in Britain’s Carboniferous strata as nodules and beds of impure iron carbonate known as Clay Ironstone. Once a valuable source of ore, alongside a dark carbonaceous form known as Blackband. In Cleveland the well-known ironstone through which which Teesside became a major industrial force from 1850, is of Jurassic age (c.188,000,000 years old), contains iron-rich berthierene rather than siderite, and occurs with a distinctive texture known as oolitic. An amalgamation of small rounded concentric structures, which form through the same colloidal processes as those reponsible for oolitic limestones, make up the bulk of the rock. Siderite can also be found in massive, granular, or concretionary forms, produced in a variety of environments including within hydrothermal veins along with pyrite and galena, within intrusive pegmatites, and as sedimentary Bog Iron Ore in high latitude lakes and swamps.

At its purest, siderite forms rhombohedral crystals with a vitreous (inclining to pearly) lustre, perfect cleavage, a white streak, and uneven fracture. An allied mineral Hydrated Iron Oxide or Limonite (FeO(OH)·nH2O), commonly forms pseudomorphs (perfect copies) of siderite crystals.

It is however more usually found in the local area as red-weathering nodules within grey mudstone scars, exposing part of the Cleveland Ironstone Formation that crops out on the foreshore at Jet Wyke, Staithes. In the 1700s, such nodules were collected from the scars by local villagers and loaded onto boats which eventually disgorged their cargoes at furnaces on Tyneside, long before the significance of the Cleveland Ironstone Formation was suspected.

Images above are of:
Manganoan Siderite with Albite;
Siderite Pseudomorphosis in Limonite with quartz;
Red Siderite Nodule in Grey Mudstone at Staithes.

Around 58 million years ago, as the Atlantic oceanic basin formed, adjacent areas of crust became stretched and weaknesses could be exploited by molten material (magma) being forced into the crust by pressure from below. This magma cooled very quickly surrounded by local rocks and became the Cleveland Dyke.

Stretching for c.350 miles between Mull in Western Scotland and the Tees Valley and North Yorkshire the hot magma cooled to form a dark blue-grey, finely crystalline rock referred to by geologists, more correctly, as dolerite. Dolerite is chemically similar to basalt, the major difference being that basalt is erupted at the Earth’s surface, whereas dolerite solidifies within the Earth’s crust.

Following removal of the overlying strata by erosion, primarily through glaciation, the dyke was exposed at the Earth’s surface. In the west of our region it can be traced crossing the river at Preston-on-Tees, but perhaps its most notable feature occurs near Great Ayton where the more durable rock making up the dyke, and softer Jurassic strata into which it is intruded, exhibit a phenomenon known as differential erosion. The softer sedimentary rock is preferentially removed by erosion leaving the harder whinstone to form a bold ridge called Langbaurgh Ridge.

The geater hardness of whinstone relative to sedimentary rock makes it ideal for use road-stone and cobbles, and it was for this purpose that Leeds City Council leased land around Great Ayton, where the ridge is best developed, in 1869. Large quantities of the rock were quarried at Cliff Rigg, as well as elsewhere along the length of the dyke, for example at Preston-on-Tees, Ingleby Barwick, and at a variety of locations on the North York Moors. The now-abandoned workings today form an unmistakeable scar on the landscape, though the former quarry’s remains allow geologists to study the effects of metamorphism, i.e. the baking of the surrounding sedimentary rock when the hot magma was injected.

Alum Shale is an unremarkable, grey, thinly-bedded, pyritic mudrock that weathers readily to thin crumbly flakes, the detritus often forming steep talus slopes below the working faces in numerous alum quarries that today reside peacefully along the coast and hills of Cleveland and North Yorkshire. The quarries and boiling houses operated for over 260 years here, commencing around 1600, in the only district in Britain where rock suitable for the important industry of alum-making was, and still is, able to be extracted.

The Tethys Sea supported a diverse fauna of, now mostly-extinct, creatures amongst which can be counted a wide-range of ammonite species, belemnites, fish, and a number of large reptiles including crocodiles, ichthyosaurs and plesiosaurs. At the end of their lives, the remains of these creatures would settle on the sea-floor and occasionally become buried and preserved as fossils. Given the rock’s mode and time of creation, who amongst us could have imagined that the remains of these leviathans, tokens of antiquity from a long lost world millions of years after their lives had ended, would once again see the light of day by way of a quarryman’s hands.

Ammonites achieved their evolutionary zenith during the Jurassic as a result of which some species are only found within a very small stratigraphic range. The usefulness of this to geologists in ascertaining the relative ages of strata was noticed by alum-maker’s son Louis Hunton (1814-1838), who collected data at coastal quarries and made valuable contributions to the young science of biostratigraphy in the 19th century.

The large reptile fossils began to come to light during the 18th century at a time when the science of geology was in its infancy. They provided some of the earliest, best preserved, fossils to be examined by early palaeontologists and found their way to academic establishments across the world. Specimens of these and many more fossils can be seen today on display in Pannett Park Museum, Whitby.

The image above shows Lower Jurassic Alum Shale (grey) making up the lower part of the cliff at Rosedale Wyke, Port Mulgrave. The overlying yellow-brown sandstone belongs to the Middle Jurassic Saltwick Formation.

Locally the Cleveland Ironstone Formation, deposited in a tropical sea which occupied the Tees Valley during the Jurassic Period around 190 million years ago, was exploited at over eighty mines between 1850 and 1962. The stone’s iron content of around 30% being much less than the high grade ore required today. Its former exploitation led to the founding of a great number of blast furnaces, shipyards, foundries, iron and steelworks along the banks of the River Tees. Cleveland Ironstone was fundamental in the growth of our region as a world centre for the iron and steel trades.

More information about the way in which Cleveland Ironstone was mined can be found on this site and via The Cleveland Ironstone Mining Museum at Skinningrove.

Mammoths have six sets of teeth throughout their lifetime. (Much like modern day elephants). They moved forward from the back of the jaw and replaced older worn out teeth as they fell out. This means that there are lots of teeth that can be preserved. Thin enamel plates cemented together. This makes a tall strong, wear resistant tooth.

They are often dredged up from the North Sea. Here they are from a land bridge between England and the Netherlands, which was cut off as sea levels rose 6 – 8,000 years ago. The teeth have then been reworked by the sea bringing them to the surface to be collected by trawlers.

The remains of a species of Dwarf Woolly Mammoths have been found on an island between Russia and North America. These have been dated back to 7,000 – 3,500 at the same time that the pyramids and Stonehenge were being built.

It is made up of a mineral called Chalcedony, this is a silica mineral with no obvious crystals. It formed either by the deposition of silica on the sea floor from animals with silica based skeletons or by replacement of rocks by silica from percolating waters long after the mineral has been deposited.

Flint is only formed in areas south of the Tees Valley. It was brought to our beaches as ballast by ships from London coming to trade on the Tees. They would dump the ballast and carry iron and steel away from the area.

Diamonds form between 120 – 200km below the surface, in the Earth’s mantle, in patches amongst mantle rocks called peridotites and eclogites. Study of these rocks tell us that the material from which diamonds form is sea floor from 2-3 billion years ago that has been subducted into the mantle. These rocks are then subjected to temperatures over 10000°C and high pressures.

Diamonds are brought to the surface by eruptions from deep within the Earths mantle. The rocks form Kimberlite pipes, which are very rare. Such eruptions bring to the surface a sample of the rocks found within the mantle and are the main source of information about the centre of the Earth. These exotic pieces of rock are called xenoliths. The explosions occasionally pass through these patches bringing diamonds to the surface as xenoliths. Diamonds only survive if brought to the surface quickly. If they travel slowly to the surface they turn into graphite.

Kimberlite pipes found within very old continental crust, underlain by cold mantle have the highest chance of containing diamonds, but a kimberlite pipe could form anywhere at any time.

Below is an image of a Harpoceras, which lived during the Jurassic Period. These fossils can be found in the Upper Liassic shale (Whitby Mudstone Formation) which crops-out widely across Cleveland and the Tees Valley. They lived in a warm tropical sea which occupied the area around 185 million years ago, alongside squid-like belemnites, marine crocodiles, ichthyosaurs, and long-necked plesiosaurs all of which have been discovered locally.

Ammonites reached their evolutionary zenith in the Jurassic and a great number of different short-lived forms existed during this Period. This resulted in fossils of each species being distributed in discrete bands within the rock record, a quality which geologists employ in correlating similar rock units across widely seperate districts.