Biodiversity

Dundee Law is the most prominent landmark in the city rising to 174m (572 feet) above sea level. Its origin dates from the Silurian (444 -419 million years old) and lower Devonian (419.2 – 393.3 million years old) periods. The Law can tell us about local and national geology and the processes that formed the landscape of Dundee.

Dundee was part of a supercontinent called Laurussia, which included present day North America, the UK and parts of Europe. During the formation of Laurussia, a part of a huge mountain range the Caledonides was formed north of Dundee.

As this mountain range was eroded rivers brought massive amounts of sediment into the area which settled and over time became a rock formation: the Old red sandstone. In the Dundee area this is called the Dundee flagstone formation (because the stone was quarried to make paving stones). The rivers did not flow all the time, so the sandstone was formed in layers.

In the same time period earth movements to the south caused the eruption of volcanoes and the movement of molten rock in the Ochil volcanic formation.

These two formations met in the Dundee region and layers of rock from each group are mixed together rather like a multi layered sandwich.

Dundee Law is a volcanic intrusion; this is molten rock that travelled underground through weaknesses in the sandstone. As it solidified underground it is called a sill. The rock is similar in composition to andesite lava, containing minerals of silicon that are rich in magnesium and iron. It is much harder than the surrounding sandstone.

On the north side of the law is the remains of a quarry and the rock face visible from the road shows polygonal columns formed as the magma (molten rock) cooled.

The Law remained covered by sandstone until the Ice Age which began about 2.6 million years ago. During that time a number of ice sheets moved across Scotland from west to east. The ice was up to several hundred metres deep and wore away the softer sandstone around the Law. This process deepened the Tay valley to the south and formed a valley to the north following the line of Strathmore Avenue.

The harder rock of the Law took the full force of the ice and the west side is almost vertical forming a crag. It became exposed when the ice retreated. To the east is a gentle slope formed by glacial debris which settled in the shelter of the crag. This feature called a tail is most visible looking along Hill Street and Kinghorne Road.

For more information please visit https://www.dundeelaw.info/timeline

The path and cycle way between Grassy beach and Douglas Terrace, shows various rock types of the Ochil volcanic formation which are valuable for education. This rock was laid down during the lower Devonian period (419.2 -393.3 million years old).

The exposures outcrop on the beach, however many of the features were covered in concrete during repairs to flyover sections along the coastal path.

From west to east starting at Broughty Ferry Road adjacent to the entrance to Dundee Port, the bedrock is pyroxene (silicate minerals) rich andesite lava. Approximately opposite Dundee Road west is a sedimentary conglomerate (also called puddingstone) consisting of small pebbles in a matrix. This is mostly hidden by beach deposits. Next to this is a section of andesite lava with a slightly different mineral composition, the centre of this is opposite Ravenscraig Gardens. There are still some small beach outcrops showing brecciated lava flows. Breccia means broken rock. It forms when the surface of a lava flow cools down and hardens forming a skin over the molten lava below. As the remaining lava is insulated it stays molten and may travel long distances. The surface often collapses and fragments fall into the molten lava below, however this lava is now too cool to remelt the fragments. When the lava finally solidifies the fragments can be seen as separate chunks in the rock.

Finally there is an outcrop of basalt (90% of the earth’s crust is basalt) just west of the boat sheds again mostly covered on the beach.

Although not listed as a geodiversity site the park has interesting geomorphological features.

Balgay Hill is another Lower Devonian intrusive volcanic sill similar to the Law. Along the Windy Glack path (under the Hird bridge) is evidence of glacial movement. The glack was an area of weakness and during the ice age, glaciers wore away a narrow fissure in the rock. As the park was developed this gap was widened along the east side. However, the rock on the west side has stayed intact. A highly polished surface and a series of parallel scratches can be seen in the rock face. This was formed as moving ice containing rocks of different sizes flowed across the rock. This ice acted like sandpaper leaving a smooth surface behind when it melted.