The Geology of Helensburgh

The geology of Helensburgh is mostly obscured by vegetation and building. A walk along the Clyde to Kidston Park will reveal more of its ancient history and evidence of a tragic near-miss. Looking across to the Rosneath Peninsula, the valley of the Kilcreggan and Camsail burn, which separates Gallow Hill at the tip from the rest of the peninsula, marks the line of the Highland Boundary Fault.

This fault, which runs from Stonehaven in the northeast, occurred over 375 million years ago and separates the relatively young rocks of the Midland Valley from the relatively old rocks of the Highlands. Rhu, Rosneath and Kilcreggan are therefore technically in the Highlands; Helensburgh sadly missed the `cut' by a few hundred metres. There are few accessible outcrops of rocks in the Helensburgh area but the walk to Kidston Park gives a good idea of what underlies much of the burgh. At low tide, the top of the beach beyond the junction with Cairndhu Avenue is clear of seaweed. The dark red sandstones and conglomerates here contain pebbles derived from the Highlands north of the town.

These rocks are dipping towards the marina so as you walk to Kidston Park, you are getting to the top of the exposed section. Just north of the steps at Kidston Park is the best outcrop of all. It is rarely covered at high tide and you can clearly see the variety of pebbles in these rocks which were deposited in alluvial fans and braided streams in the Devonian period, over 360 million years ago. The southern horizon across the Clyde gives a panoramic view of the 800 metres thick Carboniferous basalts of the Renfrewshire hills.

These form part of the Clyde Plateau Lavas which are the same age (±340 million years) as Arthur's Seat in Edinburgh. During the early part of the Carboniferous period, the Clyde Valley was the site of violent volcanic activity. The Renfrewshire Hills themselves were probably formed by fissure eruptions, literally cracks in the crust allowing liquid magma to escape to the surface. The fissures are aligned with a row of volcanic vents running from Fintry to Dumbarton and Dumbarton Rock itself is the remains of one of these ancient volcanoes.

The most accessible geology close to Helensburgh is on the Ardmore Peninsula. The peninsula is located south of an offshoot of the Highland Boundary Fault and contains outcrops of Devonian rocks along its western margin. Following the path clockwise, the first rocks visible on the shoreline are Lower Devonian brownish-red sandstones and conglomerates with pebbles derived from the Highlands to the north. These sediments have been folded and some of the folds, a trough-like syncline, can be seen on the foreshore.

Following the path northwards, the paler red sandstones with pale conglomerates are of Upper Devonian age. There is an important age gap of ±10 million years between these groups of rock when the folding of the lower section took place and the whole sequence was deposited some 360-400 million years ago. Thanks to Michael Fisher for his contribution on the geology of the Helensburgh area.

loch lomond webcam
Loch Lomond Webcam
Supported by Scottish Enterprise Dunbartonshire
Français Deutsch Castellano Italiano