The Duncryne Hill in Gartocharn (known locally and fondly as the Dumpling, due to its distinctive shape) today forms a viewpoint over Loch Lomond and is a short walk enjoyed by many. However, when it formed around 350 million years ago, the landscape surrounding it would have been somewhat different than that of today. This is because the Dumpling was formed during the Carboniferous period as a volcano, spouting molten rock from deeper levels in the Earth, and erupting them onto the surface. Examples of lava erupted from such volcanos in the local area during the Carboniferous can be seen from the top of the Dumpling in the Campsie Hills, which are composed of lava flows erupted from other local volcanic vents such as Dumgoyne Hill.
Approaching the Dumpling itself (via the path which is accessed from Duncryne Road), there is a small and abandoned quarry just off the path to the left as you reach the base of the hill, where some of the rock making up the Dumpling is exposed. At a first glance there are no obvious features to the rock, but upon closer inspection, the rock there is composed of small and broken fragments of volcanic rocks (likely basaltic in composition). These rocks are the remains of the conduit that would have fed the molten material from deep within the Earth to the surface, and therefore the Dumpling today represents a volcanic vent. From this vent, small pieces of rock debris would have erupted into the air as volcanic ash and partially molten rock 'bomb's, which fell back into the volcano as well as onto the surrounding area. The volcanic debris, due to its loose nature, had a tendency to slide back into the vent during inactive volcanic periods, clogging the vent, and in time cementing together to form a very solid mass of rock.
As you explore the surrounding region, you may notice other examples of free-standing rock masses in the region (e.g. Dumbarton Rock and Dumgoyne Hill). These are also the remains of ancient Carboniferous volcanoes, and because they are made of such strong rock, they have resisted erosion from glacial activity and weathering, leaving them standing tall and proud in today's landscape.
In the photo, the Dumpling 'erupted' again recently - but don't worry, it was just a bonfire lit to celebrate the Queen's Jubilee!
To find out more about the Gartocharn's local geology, please visit the Gartocharn Community website.