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Introduction What do the rocks tell Why are the Highlands

Have you ever wondered why Scotland’s landscape is so sharply divided into Highlands and Lowlands? us about the past? so different to the Balmaha is special to geologists because it is one of the The Highland Boundary Fault best places to study the Highland Boundary Fault. Follow A fault is a fracture in the Earth’s crust where two blocks Lowlands? a scenic trail of only a few miles on good paths along of rock have moved relative to each other. The Highland The difference in height is partly because the hard Highland rocks the shore of the loch. Here you can visit three different Boundary Fault stretches across Scotland from the Isle of have been more resistant to erosion. The Highlands have also been fragments of the Earth’s crust which have come together Bute to Stonehaven. Along the line of the fault, over 140 miles uplifted relative to the Lowlands due to vertical movements along from different parts of the globe. You will discover how from end to end, the gently rolling Lowlands suddenly give the Highland Boundary Fault. solid rock can be squeezed, folded, tilted upwards and split way to the mountainous Highlands. apart by faults. Many of these events happened over 600 Many geologists believe that the Highland and Lowland blocks million years ago, long before the appearance of the first The Highlands north of Balmaha formed in different places and that three continental fragments animals or plants on land. The rocks which today form the Southern Highlands were (called terranes) joined together around 400 million years ago. laid down as sediment at the bottom of the sea more than 600 Plates of the Earth’s crust, about 120 km thick, can move across million years ago. As the sediment piled up, the lower layers the surface of the planet, spreading apart, slipping past or colliding were compacted and slowly turned to rock. with each other. They move incredibly slowly, just a few centimetres each year, about the speed your fingernails grow. Similar processes Later, the solid rock was squeezed and folded by tremendous are occurring today in places such as Indonesia and along the San forces and became buried to a depth of about 15 to 20 Andreas Fault in California. kilometres. The heat and pressure at that depth caused the original minerals in the rock to recrystallise into new Many geologists believe that the Dalradian terrane which today minerals forming harder rocks. The mudstone turned forms the southern Highlands originated in western South America, into slate or schist, the sandstone became quartzite, and then became attached to North America before finally becoming part HIGHLANDS limestone became marble. The process by which solid rock of the northwest fringe of Europe! The Highland Border terrane is changes its structure in this way is called ‘metamorphism’. a narrow band of rock just a few hundred metres wide. It contains fossils which are more like North American fossils than European These changes to sedimentary rocks occur deep within ones. The Midland Valley terrane forms the Lowlands south of mountain belts and are occurring today beneath the Balmaha. It is covered by sedimentary rocks which were laid down Highland Boundary Fault Himalayas. In older mountains, such as the Alps, these after all three terranes came together. What lies beneath is still changes have stopped and the mountains are being actively enigmatic. LOWLANDS eroded. The final episode in the formation of our own Caledonian Mountains led to the rocks being uplifted back to What’s the evidence for terranes at Balmaha? On the trail you will be able to compare two rocks called Southern Upland Fault the surface about 400 million years ago and since then they conglomerate and breccia. Both contain large fragments of older SOUTHERN have suffered continuing erosion. They would originally have UPLANDS been as high as the Alps are today or perhaps rocks which had broken up and become embedded in sediment to even the Himalayas. Today’s Scottish form the new rocks. Highlands are just the eroded stumps. You would expect to see fragments of Highland rock embedded in The Lowlands south of Balmaha these sediments having been carried by rivers from their source The Lowlands are made of much just a few miles away. The breccia contains many fragments of a softer sedimentary rocks which have typical Highland rock called schist, however the older conglomerate never been metamorphosed and still does not. Therefore many geologists believe that when the pebbly Follow the trail in this look quite like the sediments they sediment was being deposited in the Midland Valley terrane, it was leaflet on a short journey once were. The red sandstone was not adjacent to the Dalradian terrane. They only came together in the deposited in rivers when the climate time interval between the formation of these two rocks. of discovery... was much hotter than it is today and the limestone formed in balmy It is interesting that today the professionals are not united in one lagoons. Coal formed when fallen trees view of the nature and significance of the Highland Boundary Fault Please do not damage any of the rocks you see on this decomposed in a humid environment. zone. Geology is a dynamic and ever-changing field of study. trail by hammering them as we want future generations to Climate change is not new ! appreciate them too. Conic Hill behind the National You may want to return Park Visitor Centre From another day to climb Milarrochy Conic Hill. The climb 6 8 Bay return the starts from the back way you came on of the main car park in Continue on the path to the car should drive to the path beside Balmaha and will take park at Milarrochy Bay. For the Rowardennan the loch you about an hour. The first time on this walk you are where you Schist smoothed path is easy to follow now in the Highlands! Since will see large by glacier but it is steep all the leaving the serpentinite you have exposures of the Rowardennan Pier 6 way. However the view crossed the Highland Boundary silvery folded schist 7 1.5 miles is simply breathtaking Fault although you can’t actually around the car park. as shown on the cover see any sign of it on the path The shiny silvery colour is due of this leaflet. The as the fault is now buried deep to a mineral called mica and hill is made of the underground. There are no the exposures are formed into 1.25 miles conglomerate rock you exposures of bedrock in the bay smooth humps ground down by 5 saw at the pier. The hill so if you want to see what typical glaciers during the last ice age. marks the northern edge highland rock looks like, you of Scotland’s Lowlands and sticks up because 7 the rock is tilted steeply, a bit like the lip of a bowl. If you have time explore the 5 area of bouldery foreshore which extends about 100 metres Continue on the path through This shows that rock can go south of the ranger station. The 4 the woods for about 600 metres. through many, many cycles of low cliff about a metre high Just beyond the third wooden eruption, erosion, deposition behind the foreshore is formed plank bridge look up to your and metamorphism till boulder Continue on the trail and after The fragments of rock in the of , often called right where you will see a over millions or clay. It consists of sediment you leave the gravel beach, just breccia are mostly silvery- small crag. It is an uncommon even billions of schist containing fragments of widely beyond a small stream, you will coloured which is the green rock with a soapy texture years. If you see inclined beds of a purple- same type of rock found in the varying sizes left behind when called serpentinite. It is part of go to the far a glacier melts and releases red rock at the water’s edge. Highlands just to the north. a thin group of rocks called the northwest of This rock contains very angular the sediment which had been In contrast, the conglomerate Highland Border Complex which Scotland you broken fragments of rock and you saw earlier contained no locked up in is sandwiched between the will see rock the ice. is therefore a type of sandstone fragments of these common lowland and highland rocks. You which has not breccia called a (pronounced Highland rocks. One theory is have therefore crossed a major changed for Serpentinite bretch-iya). that the sedimentary basin in geological boundary. over two billion The angular fragments of which the conglomerate was So far on this walk you have seen years. However in rock within the breccia are in formed was nowhere near the sedimentary rocks (containing Scotland most stark contrast to the rounded Highlands at that time! fragments of metamorphic rock) of the rock you fragments which you saw in deposited by rivers flowing over see has been the conglomerate. The broken land. The Highland Border rocks ‘recycled’ rock did not have enough time to are very different. They are about many times be rounded in the rivers and so 50 million years older than the and is must have travelled a shorter conglomerate and they were therefore distance from its source. formed on the sea floor rather of much than on land. The serpentinite younger age, was originally erupted as molten just a few magma beneath an ocean floor hundred million and was later metamorphosed. years! Serpentinite Crag 0.9 miles 4 Beds of sandstone breccia

Angular fragments in the breccia 2

1 Return downhill to the road and turn right. Where the road ends at the 0.7 miles From the car park go to the The metamorphic rock underlying old pier take a narrow rocky path 3 main road then turn right and the northern part of the loch is on the right beside the loch. The follow it round the north side of very hard and resistant to erosion path here is cut into a rock called the bay. Do not follow the main compared to the softer sandstone conglomerate, the same rock road as it turns right up the underlying the southern part. you stood on at the viewpoint. It is steep hill. Instead, keep to the Soil is formed by chemical made up of large rounded cobbles 3 shore-side road and look for a weathering of the underlying of quartzite, volcanic rock, and some wooden marker post on the right bedrock. That’s why the best granite, packed together in a finer- at the start of a stepped path grained sandy material. Continue on the shore-side path farmland can be found in the across the metal bridge and after which climbs quite steeply up Lowlands where the sedimentary There are several cliffs the hillside. Take it slowly – it to the right of the path The path cut into about 400 metres you will emerge rock breaks down more readily to the rock from the woodland at a long gently should take you about five to ten form fertile soil. between here and the minutes to get to the top. At the metal bridge. You will see curving bay with a gravel beach. The front cover of this leaflet The high ground is now behind you and summit you will be rewarded shows a similar view from that the conglomerate with a magnificent view across is comprised of beds the bay backs onto fairly flat fields. This Conic Hill which is the higher is because the rock beneath the bay is . which are inclined steeply Rounded hill behind you. Notice the line sandstone which eroded more easily Notice the stark contrast between of islands stretching away to to the right, roughly to conglomerate the high mountains to the north the southeast. The beds than the harder conglomerate which the southwest across the loch. forms the hilltop viewpoint. When you and the lower ground to the This line of islands indicates were deposited by large rivers south. The loch to the north is which carried sediment eroded from look out to the loch you can see the the northernmost edge of the same contrast as the wooded island of much narrower (and deeper) Scottish Lowlands marked high mountains to the northeast. The 2 0.5 miles than the southern part closer to broken pieces of rock became rounded Inchcailloch towards your left is quite by the zone of the Highland hilly compared to the flatter one ahead you. Loch Lomond was formed Boundary Fault. as they tumbled against each other in the when glaciers flowed from north powerful river currents. The sediments of you (called Inchfad). The high hills to south during the last ice age were laid down in almost horizontal beds at the far side of the loch are in the between about 2 million and 10,000 but these were later tilted up at a steep Highlands so the Highland Boundary years ago. angle following vertical movements along Fault must cross the loch somewhere 0.25 miles a fault just to the north. behind the islands. 1 8 BALMAHA BAY Start

View south to the Here Lowlands National Park View north to Ben Lomond VISITOR Centre and the highlands

Start: The national Terrain: The trail follows good paths, mainly Distance: The distance to the Toilets: There are toilets and park visitor centre in on the . It keeps close to furthest point of the walk is a refreshments available in the large car park at the shore of the loch so is easy to follow. You mile and a half, or three miles Balmaha at the start of the trail. Balmaha which can be should wear appropriate footwear as the there and back. The return In the summer months there are reached by bus from paths can be muddy and uneven in places. journey should take you around also toilets at the furthest point Balloch. The paths are mostly fairly flat but the short two hours on foot although you of the route at the Milarrochy Bay T he Tr ail detour up to the viewpoint is steep. can turn back at any point. car park.