Harlaw is part of a network of reservoirs that were built in the 19th century to supply the city with clean, fresh water. The network now extends deep into the Scottish Borders around Talla but the Pentland Hills contain numerous reservoirs. Harlaw was one of the many projects in and around Edinburgh of the civil engineer James Jardine, FRSE.
The trip out to Harlaw was motivated by ongoing work on Local Geodiversity Sites within the City of Edinburgh. However, Harlaw also has a visitor centre, biodiversity trail and grand views further into the Pentlands.
Last summer I helped to run a Young Navigators day for the local after school club based around Harlaw, so a return visit with the kids and Shadow to look at some of the areas I had not been able to explore seemed a good way to get the kids outdoors for part of the day and give Shadow a walk.
The geology is not terribly well-exposed at present but it is there and only a few hundred metres from the visitor centre. Even a limited exposure has the potential to be used to demonstrate some key geological concepts, which is why it is important to build up lists of local sites, as well as the national and international ‘crown jewels’ of the Geological Conservation Review and the geological Sites of Special Scientific Interest. As important is having the resources, both people and prose/maps, to explain the sites.
Edinburgh is is a great place to be a geologist, because there are so many exposures of rocks of different types and from a range of time intervals. It is also a great place to find out about geology, as a large number of accessible leaflets and online resources for people who want to find out about the geodiversity (the variety of rocks, fossils, minerals, landforms and topography) in and around the city.
The two best places to start, if you’re interested, are the Edinburgh Geological Society site. A large number of leaflets for the Lothians and beyond are available.
The British Geological Survey has also made some field excursion guides, which offer detailed itineraries and descriptions of geology, can be found on their Earthwise site, along with a wide range of resources on their Discovering Geology pages.