Geograph - photograph every grid square

Re NF9383 : Gneiss, Beàrnaraigh. Geologists can be more precise than that, in general. However the Lewisian Gneiss complex of the Hebrides is made up of umpteen rocks of different origins and different ages, all of which have subsequently been metamorphosed, deformed, folded, partly melted, recrystallised and mixed up with each other over about 3000 million years. It is often possible to date a particular band of rock in the Lewisian Gneiss to within a few tens of millions of years, but you can't get much more precise than between 3800 and 1200 million years old if you are talking about the whole lot collectively.

542 million years ago is the transition from the Archaean, which includes Lewisian Gneiss and Torridonian Sandstone among others, to the Cambrian, which is the first part of the Palaeozoic. The last tectonic event to affect the Lewisian Gneiss was before the deposition of the Torridonian Sandstone, about 1200 million years ago.