The tunnel was driven through granite, quartzite, gneiss, and shale as well as layers of sandstone, coal, and limestone.
en.wikipedia.org Second, the lower middle member is composed of purple cross-bedded quartzite, sometimes is subdivided into two units, and overlies the lower member.
en.wikipedia.org Based partly on seismic refraction traverses, a ridge underlain by dolomite and quartzite was deemed to be stable enough for construction.
en.wikipedia.org The rock is an extremely hard quartzite derivative, and is characterized by painfully sharp edges, vanishing cracks, steep slabs and small horizontal roofs.
en.wikipedia.org Some of the quartzite contains fossilized worm burrows and is known as "pipe rock".
en.wikipedia.org