In my paper on Glacial Erosion lately laid before the readers of the Geol. Mag. (pp. 323 and 356), I have endeavoured to prove that the origin of nearly all the more prominent surface characteristics of the rock scenery in the Yorkshire Dale District admits of a simple and complete explanation by the theory of the modification of pre-existing subaerially eroded surfaces by Glacial Erosion. At the same time it was shown that the character of many of the phenomena is entirely opposed to any theory of their origin by means of Subaerial Denudation alone. In the present communication it is proposed to inquire how far this Glacial Erosion theory may be applied to explain the origin of the deep, semicircular recesses that are commonly found in all well-glaciated mountainous districts, and are variously known by the names of Coums, Corries, or Cirques.