It is now 8 years since I commenced observations upon the Glacial phenomena of the Cleveland area—using the term in its broadest sense as including the whole of the Jurassic mass of North-eastern Yorkshire, but no results were attained in the first 5 years. The investigation, however, of a tract of country on the western edge of the Yale of York familiarized me with many of the more patent signs of old glacier-lakes, especially the phenomena of abandoned overflows, and this experience enabled me to recognize the great Newton-Dale valley as belonging to this category. Following this clue backward, I discovered the great system of lakes and related phenomena now to be described.