Extract
Two publications by Grabau, which will be treated in the following pages, have led to the ensuing considerations.

In his opinion world-wide advance and retreat of the sea are simply explained by vertical movements of the sea-level. About the possible cause of these movements he makes some very brief remarks, as we shall see later. It is, however, quite possible that the explanation must be sought in simultaneous but opposed movement of continents and sea-level. In trying to obtain an insight into the cause of these movements, rhythms of an entirely different sort come up for discussion, viz. phases of diastrophism and magmatic cycles. And then a further question presents itself: can these different phenomena be connected, and thus give an insight into certain rhythmical processes in the deeper parts of the earth ? I, personally, am convinced that we must answer this question in the affirmative. Stille, Joly, Holmes, and Bucher have reached a similar conclusion by different ways. Meanwhile, the following pages are only intended to shed some light on the different aspects of the problem, and I shall restrict myself to outlining the questions that demand further study.