A geological sandwich

A geological sandwich. . , A geological sandwich , Sreath air muin sreath , For many people, this is one of the grandest views in Britain , and for geologists it's also one of the most exciting! Look at the scene across the loch and you can see two lines running across the mountain These form the boundaries between two very different rock types that tell us a lot about how this area was formed. , Dha mòran, is e seo fear dhe na seallaidhean as fheàrr ann am Breatainn , aqus e tarraingeach dha-rìribh do gheòlaichean! Thoiribh sùil thar an locha ach am faic sibh dà loidhne a' ruith tarsainn na beinne. 'S e crìochan a tha seo eadar diofar seòrsa chlach a tha ag innse mòran air cruthachadh na tìre seo. , An underground shuffle , The lower of these lines marks where a landscape carved in ancient gneiss joins with quartzite. The quartzite was originally sea sand which through time became rock. The upper line is the Glencoul Thrust. This is a major ‘fault’ that formed as great upheavals in the Earth's crust forced a sheet of gneiss from the east so that it moved west wards up and over the quartzite. , What happened here was a bit like a massive deck of cards being shufled underground. Forces within the Earth caused great sheets of rock to slip and slide over one another along these thrust planes. , Dannsa fon talamh , Tha an tè as ìsle dhe na loidhnichean seo a' comharrachadh far a bheil an gneiss aosmhor a' coinneachadh ri cloich-èiteig. B' i gainmheach mhara' a bh' ann an clach-èiteig, a dh'fhàs na bu chruaidh tro na linntean mòra. ‘S e ‘Glencoul Thrust’ a th' air a' loidhne àird. Bha seo na loidhne-sgàinidh mòr a thàinig gu bith nuair a chuir gluasadan mòra ann an sgrath na cruinne siota mòr, gneiss gu siar agus thairis air siota cloich-èiteig. , Bha na thachair an seo coltach ri seòrsa paca mòr chairtean-cluiche fon talamh le cumhachdan na cruinne a' cur nan siotaichean-cloiche fo agus thar an cèile mar gum biodh iad nan cairtean dìreach. , Oldest on the top - and bottom! , Take a closer look at the Glencoul Thrust. We would expect to find younger rock sitting on top of older rock. But here we have a sandwich of sorts, where 'young' 540 million year old Cambrian quartzite is sandwiched behween layers of ancient Lewisian gneiss, which is about 3,000 million years old. , Aosda air a' mhullach, aosda air a' bhonn! , Thoiribh sùil a-rithist air an Glencoul Thrust. Shaoileadh gun lorgadh sinn a' chlach ùr a' laighe air muin na seann chloiche. Ach tha an Lewisian gneiss (a tha mu 3,000 millean bliadhna a dh'aois) a' laighe mar dhà phìos arain le sreath de chloich-èiteig Cambrian (nach eil ach 540 millean bliadhna) sa mheadhan. , Did you know? , Geologists were very puzzled by the shuffled layers of rock in this area in the 19th century. A debate raged as they attempted to understand what had happened. Visit Knockan Crag visitor centre to find out how the riddle was solved. , An robh fios agaibh? , Chuir e iongnadh mòr air na geòlaichean nuair a lorg iad am measgachadh àraid seo de dhiofar seòrsa chlach san 19mh linn. Bha deasbad mòr a' dol eatorra agus iad airson dèanamh a-mach dè thachair. Theirigibh gu ionad tadhail Chreag a' Chnocain airson fiosrachadh air fuasgladh don duilgheadas seo.