Geology and geological processes form the foundations for why the Solway Firth exists in its current form. Geology has impacted the ecosystems which have developed, the industries which can thrive, and the communities which settle in the surrounding area.

Vertical strata at Monreith


Over 400 million years ago (Silurian Period) there were two continents. These continents were located to the North and South of the Lapetus Ocean. The land we now know as Scotland formed part of Laurentia, and England, Avalonia. Over the course of millions of years these continents moved closer together. Eventually, these two land masses collided, contributing towards the creation of Pangea by 250 million years ago. The fine silts and sands on the ocean floor were folded and stacked to form the mountains we now know as the Southern Uplands of Scotland. During this process, superheated molten rock, or magma, rose and cooled, producing granite mounds under the Earths crust. As surrounding softer rocks weathered away these granite hills became exposed and today they are known as Criffel and Screel Hill on the Scottish Solway shore. The origins of Scotland and England, as part of two different continents, helps to explain the differences in geology seen in two countries geographically close in the present.

340 million years ago (Carboniferous period) the Solway was near the equator and repeatedly cycled through shallow seas and swampy forests. The remains which are preserved today as coal seams resulted from the compression of vegetation by sediments. Tropical seas, stones, sand and mud on the coast allowed layers of sedimentary rocks such as limestone, sandstone and mudstone to develop.

Overview of the Geology of the Solway Region

260 million years ago (Permian period) the Solway was an arid desert, forming red sandstone. This is still quarried in Dumfries and Galloway today and is a frequently seen in local features and buildings.

Permian rocks in Loch Ryan


210 million years ago (Triassic period) the Solway was still hot with seasonal monsoons that washed sand into layers and then cemented to create sandstone.

Over the last 1.6 million years, the Solway was reshaped into what we see today. Glacial periods scoured valley bottoms and exposed layers of rock. The weight of ice during the last ice age caused land to sink. Now that the ice has melted some land is now slowly rising due to gradual post-glacial rebound. The Solway is one of these areas still rising, offsetting a portion of sea level rise. This rebound will lessen over time, eventually stopping entirely.

To this day the ‘Solway Line’ is the geological boundary which separates Scotland and England and marks the fault where these once separate continents joined. Maryport also features a fault line between Triassic rocks and older Carboniferous rocks with coal containing outcrops.

British Geological Survey have have many resources including an interactive map viewer where you can explore the Geology of Britain.

Scottish Coast

In terms of solid geology on the Scottish side of the Solway, there is a variety of Granite, Lower Coal Measures, Ordovician – Silurian, Lias, Permian Sandstone, and Triassic Sandstone.

Silurian and Ordovician strata predominate from the Mull of Galloway to Abbey Head, near Dundrennan. From here the exposed strata is lower Carboniferous as far east as Cummertrees. More recent deposits of Permian sandstone overlie these, and have been eroded to form the lower lying areas at the head of Luce Bay, and Lochar Moss south-east of Dumfries. The remaining coast inland to Carlisle is characterised by the low, gently rolling landscape overlying triassic sandstone.

Dramatic intrusions of volcanic origin dominate the area south-west of Dumfries to form the granite hill of Criffel, Screel Hill south of Castle Douglas, and Cairnsmore of Fleet between Gatehouse and Newton Stewart. A further, isolated example of granite is to be found in the far west at Crammag Head beyond the Mull of Galloway.

Granite near Dalbeattie


Looking at superficial deposits, the Scottish side of the inner Solway is primarily made up of raised tidal flat deposits to Annan in the east, with some salt marsh present from this point to Gretna. Other deposits seen in this area of the coast include raised beach deposits, with marine beach deposits at Barnkirk Point and Powfoot, and are also from the Flandrian interglacial stage of the Quartenary period. The intertidal area consists of a variety of salt marshes, intertidal sand flat deposits, and intertidal sandbank deposits.

English Coast

On the English side of the Solway there is a variety of Middle and Lower Coal Measures, Millstone Grit, Permian Mudstone, Triassic Sandstone, and Triassic Mudstone.

Along the inner Solway Estuary both the English and Scottish shores appear similar in character, exhibiting low shores and wide mud flats at low-tide.

The underlying rock of both sides of the inner Solway are of the same Triassic era but with the younger mudstone sediment giving rise to the low lying mosses of Burgh-by-Sands.

These mudstones continue south as far as Dubmill Point where the Triassic Sandstone of the Annan area re-occurs round the whole sweep of Allonby Bay to Maryport. The sandstone has been eroded away by glacial action to reveal the older rocks of the middle coal measures giving rise to the heavily industrialised area from Maryport to Whitehaven. These strata have been deformed and displaced by volcanic activity within the central lake district to form, in simplistic terms, an inverted basin or dome which has undergone modification by various glacial events. This has led these middle coal measures to be scoured away, toward their mid point at Workington, to reveal outcropping lower coal measures. This coal bearing strata is composed of successive layers of coal, shale, sandstone bands and grey mudstones of varying thickness, all heavily faulted.

The coastline south of Whitehaven logically mirrors that north of Maryport by the re-occurrence of the Triassic sandstones but at a greater elevation above present sea level. The characteristic red rock cliffs of Saltom Bay and St Bees Head mark the southern boundary of the Solway Firth Partnership area.

Looking at the superficial sediments of the inner English Solway from the Scottish border, west to roughly Seaville, artificially induced alluvial deposits, raised tidal flat deposits, till, and raised marine beach deposits make up most of the Cumbrian Solway coastal deposits. The intertidal area of the Solway, similar to the Scottish side, is primarily salt marsh and intertidal sand flat deposits.

From Grune Point to Wolsty, storm beach deposits, marine beach deposits, and blown sand are the primary coastal deposits on this stretch of coastline. The intertidal area, similarly to the area discussed above, is primarily made up of intertidal sand flat deposits, with Stenor Scar and Grune Point being highlighted as Diamicton, and Stenor Scar being from the Mercia Mudstone Group.

Siddick rock formation

Impacts of Geology

As previously mentioned, geology can have a huge impact on settlement patterns, industrial, and agricultural activities. The Solway has traditionally been exploited for coal on the English side as extensive parts of the Solway Basin overlay Carboniferous rocks including Westphalian Coal Measures. The deep burial of these rocks has led to the generation of gas and oil. Other valuable formations are typically extracted, such as granite or sand. However, the results from this process can cause environmental impacts such as increasing air and noise pollution, among others. The past has seen lucrative mining and quarrying of materials surrounding the Solway coast, such as coal, sand, gravel, and granite. Sand and gravel mining continue to take place around the Solway, for example in Sandhead, Dunragit, and Hoddam Contracting’s Broom Quarry, near Powfoot.

Granite quarry near Creetown


The mining of metals such as lead, zinc and copper deposits has been relatively common throughout Dumfries and Galloway. Although extensive mining activities occurred at Leadhills (just outside of Dumfries and Galloway) inland of the Solway, several mines operated in areas closer to the Firth, such as near Gatehouse of Fleet. In 1770, chalcopyrite, malachite and azurite were reportedly present and being mined at a coastal location near Colvend, while Baryte mines at Barlocco (producing ~3000 tonnes) and Auchencain (producing ~700 tonnes) were in operation between 1856 and 1920, and in the 1860s respectively (Stone et al, 2012).

Uraninite is also present and has been the topic of studies at the Piper’s Cove/Needle’s Eye, south-west of Caulkerbush.

It is also worth noting that climate change, which is producing warmer temperatures, may increase loss of organic matter from soils, contribute to greater coastal erosion from increased rainfall and sea level rise. In turn this may alter geology in terms of eroding rocks or deposition.

Cultural Geological Features

Much like other features around the Solway, geological features have long standing stories attached to them. Unique geological features form part of history through place names, location markers, and form an important part of traditions and folklore still passed down today. As with many of these features around the Solway the following are just two examples of how geology remains an important part of the heritage and culture today; the Devil’s Stane, and the Altar Stone.

Devil’s Stane

The Devil’s Stane sits on the coast at Powillimount, with little explanation for why this granite boulder is located here. Legend says that the Devil took a bite out of Criffel and, disliking the taste, spat out this chunk. Supposed proof of this story lies in the ‘teeth marks’ which can be seen on the top of the stone. These marks are actually abandoned work to split the rock.

The Devil’s Stane, near Carsethorn


Altar Stone

The Altar Stone is a boulder on the sands south of Annan that has been a boundary marker since medieval times. The stone marks the parish and Royal Burgh boundary as well as defining fishing rights. It is also the target mark for riders in Annan’s Riding of the Marches, when tides allow for this. The Altar Stone is not always visible, at times covered by the shifting sands of the Solway, but its position is still used for these purposes.

The Altar Stone, Annan


For more information please see Solway Firth Partnership’s Coastwise Project (concluded 2019), which sought to find the origins of place names on the Scottish side. Place name origins are often connected to the geological features of an area, such as Rough Island/Firth, where the granite outcrops form a rugged coastline, and is likely the reason behind the origin of ‘Rough’ meaning uneven.

To learn more about Scotland’s geology visit the Scottish Geology Trust

To learn more about geology in Cumbria visit the Cumberland Geological Society