The geology of the county is dominated by a number of physical and geological features. To the west is the Hampshire Basin, along its north and NW side are the deposits of the Thames Valley and Basin, to the NE and east are the chalk hills of the North Downs, whilst in the south are the older rocks of the Weald. These have given rise to the marked topographic changes encountered throughout the county.

The pattern of underlying strata has greatly influenced the course of rivers and hence the siting of settlements and lines of communication ( today north-south roads still pass through the gaps in the North Downs cut by meltwater rivers during the ice ages). Meanwhile the rocks themselves play a major part in influencing soil type (and therefore fertility), and most importantly drainage. The presence of spring lines at the base of the chalk on the downs has been another historical influence on the siting of settlements. However, the lack of water on the on the porous chalk downland above has influenced land-use - this being suitable for grazing sheep but prohibitive for arable farming. In places the sandy, acid soils of the Weald or of Surrey Heath are even poorer, and are dominated by heathland and forest. Light clay or sandy soils however do exist on the Greensand and Gault at the foot of the Downs, in some parts of the Weald, and on the London Clay and sand and gravels of the Thames Valley and these areas have been more intensively farmed. Exploitation of natural resources has in the past contributed greatly to the local economy. Even today, sand and gravel extraction is still important along with minor amounts of quarrying for chalk and clay.

The oldest rocks which outcrop within the county are the uppermost beds of the Tunbridge Wells Sand of Wealden age. These rocks are approximately 130 million years old and outcrop around Lingfield and Felcourt. They are not very fossiliferous.

Overlying these is the Weald Clay which outcrops much more extensively within the area. It underlies much of the gently undulating country in the south of the county. Outcrops of this can be seen in the Hindhead-Haslemere area in the SW, in the Mole Valley area (it forms much of the scarp slope of Leith Hill and has been quarried in the Ockley-Capel area to the SW of Dorking), and again south of Reigate and Godstone further east. The beds of clay are quite thick in places and are interbedded with thin lenticular limestones crowded with gastropods - the so-called 'Paludina limestone'. These sediments were laid down within a succession of vast freshwater lakes which covered this part of southern England between 120-130 million years ago. Dinosaurs such as Iguanodon and Baryonix (the recently discovered Surrey dinosaur or "Claws") inhabited the lands around the margin(s) of the lakes. Their remains and that of freshwater fishes, insects such as dragonflies, and plants have been found in Surrey - particularly from the brickpits and other excavations around Capel, Ockley, and Charlwood.

The various beds of the Lower Greensand are particularly well represented within the county. These beds of sediment were laid down between 120 and 100 million years ago as shallow seas inundated the landmasses once more. Britain was then much closer to the equator. The lowermost unit of the Greensand is the Atherfield Clay - named after Atherfield Point on the Isle of Wight where these beds are well developed. In Surrey these beds have a much limited exposure although they outcrop along the base of the Greensand escarpment where the impermable clays act as a spring line and form much of the boggy land in the valley bottoms. This can be seen at the base of Leith Hill and in the bottom of the Devils Punchbowl at Hindhead, whilst the clay itself can be seen in brickworks at Reigate, Littleton, and Haslemere. The clay is quite fossiliferous in places.The Perna Beds are concretionary masses which are sometimes crowded with fossils that lie at the base of these clays at Reigate. Like so many other localities they are no longer accessible.

The Hythe Beds are more extensive and their outcrops rather more obvious. A number of the sandstones include beds of chert (a form of silica like flint) which makes them more resistant to erosion. The outcrops tend to form prominent ridges or escarpments and the highest hills in the county (Leith Hill [967 ft.] and Gibbet Hill [895 ft.]) are capped by it. The rocks are typically 'cleaner' quartz sands and rather unfossiliferous apart from beds of microscopic sponge spicules.

Resting "unconformably" upon the Hythe Beds are the various contrasting rock types of the Sandgate Beds. At its base ,the concretionary calcareous sandstones of the Bargate Beds outcrop, yet the distribution of these is fairly well restricted. They are well developed in the around Godalming (named after Bargate in Godalming) where the beds were quarried as a good local building stone, but they don't appear to outcrop further east than Abinger. In places they are well fossilised and some large ammonites (Parahoplites sp.), nautiloids and other invertebrate fossils have been collected.

In another variation the Sandgate Beds include 50-70 ft. of soft sandstone alternating with fullers earth clays. This development is fairly unique and the Fuller's Earth Beds outcrop in is limited to a small area between Nutfield and Redhill. The montmorillonite clays have unusual degreasing and cleaning properties which have made them ideal for the purpose of 'fulling' wool. The beds here have thus been worked since medieval times and it has always been an important local industry. There are still some quarries open and the clays are now used for cleaning oil, pharmaceuticals, and in colouring. The clays contain some interesting residual minerals as well as occasional nodules of honey coloured barite (barium sulphate) mineral. Fossils including ammonites (eg. Parahoplites nutfieldensis), bivalves and fossil wood are not uncommon.

The topmost beds of the Lower Greensand are known as the Folkestone Beds. These are often quite coarse grained rocks and these include current-bedded sands, frequent bands of iron-sandstones ('carstone'), and in places outcrops of leached, pure silver-sands. The latter have been quarried for glass-making, but most extraction is now for builders' sand used for making mortar. There are underground quarries at Reigate and Dorking. The Folkestone Beds form the high ground around Guildford (St.Martha's Hill) and the iron (ferruginous) sandstones the landmarks of Crooksbury Hill and the Devil's Jumps near Frensham. The beds are typically unfossiliferous.

The Gault Clay which overlies the Lower Greensand was deposited under deeper water conditions as the 'Wealden' landmass gradually subsided during the later Cretaceous. The stiff blue-grey clays of the Lower Gault and pale marly clays of the Upper Gault were lain down between 110 and 97 million years ago. The formation is in some places very fossiliferous and is rich in ammonites, bivalves, gastropods, and belemnites, and sometimes wood fragments, fish teeth, and crustacean and sea-urchin remains. The Gault has been (vertically) zoned on the basis of its ammonite fauna. The clay outcrops all the way round the north and NE edges of the Weald beneath the chalk escarpment, although it reaches its greatest thickness and development between Reigate, Godstone, and Caterham in the east. In the neighbourhood of Reigate it forms the Vale of Holmesdale. The impermable clays carry many streams and the marly clays of the Upper Gault in particular forms good agricultural land. The Gault reaches its maximum thickness of 343 feet at Caterham. In places the clay has been quarried for the manufacture of local bricks and at Wrecclesham there was once a pottery.

In places the Upper Gault has been replaced by the Upper Greensand formation. We know that these two formations were largely contemporary in age since they have some of the same fossils. The Upper Greensand was deposited under rather shallower near shore conditions. The Greensand is so-called on account of the presence of grains of a green phosphatic mineral called glauconite. It is present as a very narrow outcrop along much of the North Downs, broadening out to the south and west of Guildford, whilst in the east around Merstham and Reigate it forms a small but prominent escarpment. Here the calcareous malmstone or 'firestone' was formerly worked by means of underground galleries and was a much sought after building stone. A softer bed of rock the 'hearthstone' was quarried for use as a domestic scouring stone. Within the Upper Greensand can be found a number of sand-loving species of fossil mollusc.

Although it might appear to be all the same, the Chalk formation of the Upper Cretaceous is actually divided up into three distinct units: the Lower Chalk, Middle Chalk, and Upper Chalk. Typically the chalk is a soft white limestone rock composed of the shelly remains of microscopic plants (coccoliths = algae) and animals. The remains of larger fossils - such as sea-urchins, bivalves, sponges, and ammonites are sometmes common. The chalk was deposited under oceanic conditions at a time when the seas covered most of Britain and much of the continent (between 97 and 65 million years ago). It is the chalk which is responsible for the characteristic relief of the North Downs, the feature which is most readily identified with the geology of the county.

The Lower Chalk is most frequently exposed in pits on the chalk escarpment of the Downs as well as those in the vallies beneath - as at Oxted, Merstham, Godstone, Betchworth, and Dorking. At the base of the chalk is the Chloritic Marl. Typical fossils include the ammonites Schloenbachia and Mantelliceras and the sea urchin Holaster subglobosus. Fish and reptile remains are occasionally found. Its maximum thickness at Caterham is about 150 feet.

The Middle Chalk is more often exposed on the scarp face of the chalk escarpment. For this reason it is less often visible at close hand within many of the quarries that cut it. At its base is the Melbourn Rock, a hard band which sometimes forms a prominent spring line. Brachiopods (or lamp shells) such as Orbirhyncia cuvieri and Terebratulina lata are the 'zone fossils' of the Middle Chalk. Geologists use these as a means to date and identify it. Good exposures of the Middle Chalk once occurred in quarries at Dorking, Betchworth, and Merstham, and it also outcrops beneath the landscape at Worms Heath, Warlingham, Woldingham, and Caterham, and in the west on the Hogs Back. It reaches its maximum thickness at Caterham (up to 200 feet).

The Upper Chalk tends to be more fossiliferous - or at least more fossils are seen and collected from it since many are preserved in flint which occurs both in nodules and tabular masses within it. Flint is re-deposited silica. The silica has probably been derived from the solution of fossil sponges, some of which are abundant within the upper parts of the formation. Pyrite nodules - rusty brown, heavy, ball-like concretions - are also common. Typical fossils include fragments of the bivalve Inoceramus lamarcki and the heart-shaped sea urchin Micraster and dome-shaped urchins Conulus and Echinocorys. The flint layers are commonly associated with these echinoids. On the Downs the Upper Chalk more often than not forms the shallow dip slope of the escarpment and this may be exposed in small quarries, road-cuttings, and the fossils within residual flints lying on the surface. At its maximum thickness towards the western end of the Downs the Upper Chalk is about 550 feet thick. It is well exposed at Caterham, Epsom, Box Hill and Dorking, E of Guildford, and to the SW on the Hogs Back.

At the end of the Cretaceous and beginnning of the succeeding Tertiary period the ripple effect of widespread earth movements associated with the uplift of the Alps in Europe, gently folded and lifted the rocks of the Weald into a dome. Over time the central part of this (occupying the areas of S Surrey, Kent, and N Sussex) eroded down exposing the older rocks beneath. The younger and slightly more resistant rocks such as the chalk were thus left upstanding around the flanks , dipping (northwards) away from the centre.

The lowest (oldest) bed of overlying Tertiary which outcrops is the Bull Head Bed of the Thanet Sand (Palaeocene age - 60 million years old). The Bull Head Bed (only 9" thick) and overlying sands (10') outcrop in a narrow band between Leatherhead, Ashted, and Epsom. It is unfossiliferous.

The Reading Beds of the succeeding Lower Eocene formations (57 million years) outcrop in a number of places on the Downs - generally as isolated patches or outliers. Typically these are red and green clays with occasional beds of oysters and other shells - most of them very different from those of the chalk. These impersistant beds outcrop in numerous locations such as at Headley, Ashtead, and Effingham in the Dorking-Reigate area, and also along the North Downs including around Guildford and the Hogs Back. Overlying the Reading Beds are to be found occasional outcrops of Blackheath Beds. More commonly developed in SE London and Kent these can however be seen at Croham Hurst and Caterham.

To the north of the Downs lies a syncline or basin of deposition - in geological terms this is commonly referred to as the London Basin. Overlying the buried chalk beds beneath London and the NW part of Surrey (Bos. of Spelthorne, Runnymede, Elmbridge, Surrey Heath, and Woking) are up to several hundreds of feet of London Clay. The maximum thickness of this is reached just outside of the county ( up to 400' beneath Esher and Wimbledon), but in the NW of Surrey this is overlain itself by later Tertiary and Quaternary deposits. The London Clay and its fossiliferous remains were deposited in a tropical sea that covered the London Platform (as well as Surrey) between 55 and 52 million years ago. Although London Clay fossils tend to be infrequent finds within the fossil collections of Surrey's museums they are in fact common almost anywhere the clay is exposed in excavations or quarries. Remains of the large 'pearly'nautilus Cimonia imperialis is sometimes found along with bivalves, gastropods, crustacea, fossil wood, fish teeth, and on occasions mammal bone. Concretions known as septaria, pyritised wood, and clear crystals of gypsum (selenite) commonly occur.
Whilst actual outcrops may be restricted (for London Clay typically forms areas of low-lying land) it nevertheless underlies a significant area of the county from Epsom in the east, to north of Leatherhead, and then westwards across the whole of NW Surrey. Claygate in Surrey gives its name to the Claygate Beds (sandy transition beds at the top of the London Clay) which was formerly quarried as a brick clay.

In the NW of the county Middle and Upper Eocene clays and sandstones form the heathland of Surrey Heath and Chobham Ridge and also outcrop to the east at Runnymede, Chertsey, near Weybridge, and as far east as Painshill Park.

The Bagshot Beds (50 million years old) consist of different coloured sands, seams of pale pipe-clay, and local beds of flint-pebble gravel. Here they probably don't exceed 100 ft. in thickness. Fossils are rare and are restricted to plant fragments and marine shells.

The Bracklesham Beds (47 million years old) are divided into laminated clays, glauconitic and coloured sands,and pebble beds. An ironstone band at the base of these beds was once worked as a source of iron at St.Georges Hill near Weybridge, whilst red clays were quarried for brickmaking near Bagshot. These produced the so-called Bagshot or Rubber Bricks. Fossils such as bivalves, gastropods, and nummulites are occasionally found.

The Barton Beds ( 44 million years old) consisting of yellow sands, pebble beds, an ironstone, and loams are now only preserved as small patches or outliers where they have escaped erosion - such as on St.Georges Hill and Chobham Ridges where these are best developed. Bivalves and gastropods are only present as hollow casts and are generally rare.

Oligocene and Miocene rocks appear to be absent from the area. Sediments of these periods (particularly the latter) are apparently rare in Britain. Although they would almost certainly have been deposited, most of such sediments were probably removed during the later Pleistocene (Ice Ages) period through glacial action.

There is some debate as to the extent of surviving deposits of Pliocene age (2-5 million years old) on the North Downs. Small patches of sediment similar to the Reading Beds, as well as Pebble Gravels, and Clay with Flints , overly both Reading Beds and the underlying chalk. Small patches of these various later deposits are to be found at Netley Heath near Guildford, Ranmore, and Headley Heath near Reigate. Fossils of Red Crag (Lower Pleistocene) age have been found in deposits at Netley Heath suggesting that marine deposits of this age may once have been deposited on top of the chalk.

Whilst no true glacial (moraine) deposits such as chalky boulder clay are to be found on the North Downs or further south, the furthest extent of the earlier ice sheets over southern Britain during the period of glaciation (intermittant between 500,000 and 15,000 years ago) remains somewhat ambiguous. There is however much better evidence for glacial outwash gravels (Plateau Gravels such as cover Epsom Common, Great Bookham Common, Chobham, and at Newdigate) and permafrost chalk soils and rubble (Coombe Rock) and frozen gravels (Taele Gravels as found at Great Bookham, Ashtead, Epsom, Brockham and Betchworth).

River gravels such as occur in the Thames River Terraces (Flood Plain, Taplow, and Boyn Hill Terraces) can occupy large areas. The earlier terraces which may have been formed more than 250,000 years ago were deposited at a higher level before the downcutting of the bed of the river. Most of the surface geology within the Bos. of Runnymede, Spelthorne, and parts of Elmbridge relate to these terrace gravels of the Thames and this has also become an important economic resource in terms of sand and ballast gravel for the construction industry. Gravel extraction, both old and modern, has resulted in the discovery of Pleistocene mammal remains including many examples of cold-living fauna such as woolly mammoth, woolly rhinoceras, red deer, reindeer, wild horse, aurochs etc. Most of these finds have been of disarticulated remains since these would often (though not neccesarily) have been washed downstream by the river. Although modern methods of gravel extraction through dredging does not favour the preservation and discovery of such fossils, remains of mammoth teeth and tusks, bones etc. are still deposited with museums and form a useful if partial record of animal distribution. River Terraces and gravel deposits, though much reduced in comparison, occur on most of the large Surrey rivers - in particular the Mole, the Wey, the Blackwater and others. Excavations for gravel or construction have produced similar finds of Pleistocene mammals, mammoth teeth being amongst the commonest finds deposited in nearby museums. Not all such finds have been from river terrace deposits and locality details in these cases can prove extremely important.

Other late Pleistocene deposits include the Brickearth (wind blown loess deposits and alluvium) some deposits of which have produced sub-fossil mammal remains. Brickearth is of fairly wide occurrence in the valley of the River Mole near Dorking and Betchworth.
Dry Valley Gravels occur in a number of locations [ such as in the Caterham valley and Kenley] and may be of Pleistocene or more recent Holocene age (12,00 years to present).
Other deposits of hillwash loams and river alluviums are all of more recent (Holocene) origin.