Ars longa, vita brevis. This is especially true when one reaches the age of 64. I therefore commit to paper some of the results of a geological investigation of Snowdon on which I am engaged. I start of course from the work of Messrs. Ramsay and Selwyn embodied in the Geological Survey Map of Snowdon and Ramsay's memoir on North Wales. To make what I have to say clear I may state that the rocks of Snowdon are by Ramsay and Selwyn divided into three principal groups, viz.: A, an upper felsitic lava ; an intermediate band (B) of bedded fossiliferous rocks of Bala age, containing much volcanic material, called the calcareo-felspathic ashy series ; and a lower mass (C) of felsitic rocks. This lower mass is in some places divided by sedimentary bands consisting of slates and grits. Below C come blue slates and grits, with occasional volcanic bands, D; and below D the great mass of volcanic rocks (E) which form Glyder Fach and Y Tryfan.