Newry and Mourne is a classic area in terms of the field mapping of various types of granite and interests geologists all over the world. One of the most remarkable granite mapping achievements ever made anywhere was by J.E. Richey during a mere six weeks in the summer of 1925 (published in 1928). He totally transformed the geological map of the Eastern and Western Mournes from ‘just two simple red blobs’ (the colour often used on maps to designate granite) into one showing five different types. Each was emplaced as a separate injection (intrusion) of granitic magma rising from deeper in the Earth – three in the east with the first G1 followed by G2 and G3 and then two in the west, G4 and finally G5. These granite magmas did not reach the surface so there was no related Mourne volcano; rather the overlying sedimentary rocks were eroded down eventually to reveal the granites. Historically, this was the first use of the ‘G nomenclature’ now standard in designating the time sequence of granite emplacement for any region of the world.

Each Mourne granite had crystallized and was relatively cold before the next one arrived: later work has shown that after G1 each granite was emplaced not as a single injection but by a series of rapidly sequential ‘squirts’ referred to as pulses by granite geologists. These pulses can be distinguished and mapped by careful field study as indicated on our most recent geological map of the Mourne Mountains (work in progress by the MGAG).