WHILE the atmosphere is the most active of all geological agencies, it has received the least careful study from geologists. Its very activity destroys its relics almost as soon as formed and gives them peculiar evanescence. This has invited the neglect of geologists laudably prone to concentrate their attention upon agencies which have left enduring and unequivocal records. The atmospheric element in geological history bids fair to long remain obscured by elusive factors and uncertain interpretations. None the less it is an element of supreme importance and should be persistently attacked until it yields up its truths. This must be my excuse for offering a paper which, I am painfully aware, is very speculative in many of its parts. All our attempts at the solution of climatic problems proceed on some conscious or unconscious assumption concerning the extent and nature of the atmosphere at the stage involved. These assumptions are too often unconscious and the conclusions reached command a confidence which might not be reposed in them if the underlying assumptions were frankly stated. It may not be unwholesome, therefore, to raise some radical doubts respecting current assumptions regarding the early stages of the