The following remarks were written for the Settle Caves Exploration Committee in the spring of 1871. They were subsequently submitted to the British Association in 1872, and are, with additions embodying the result of the latest explorations, offered to the scientific public. First, I propose briefly to describe the beds with which we have become acquainted in the course of the explorations, their apparent range and superposition. Secondly, I will endeavour to show to what natural causes they probably owe their origin.