INTRODUCTION This chapter surveys mass mortality in the sea, its causes, and its significance to paleontology. Section I discusses mass mortality in sea and a few examples of mortality in inland waters (rivers entering into salt lakes, etc.). Various causes of these phenomena are discussed. Surveys of the literature concerning one of these causes (noxiousness of waterbloom) were published by Brongersma (1948) and Galtsoff (1948 and Galtsoff (1949); the paleontological significance of mass mortality by red water has been discussed by Brongersma (1944; 1947; 1948), Falke (1950, p. 64), Gunter (1947b), Pratje (1949), and Richter (1950). The present survey is certainly not exhaustive. Furthermore, the cause of some mortalities is still uncertain. In paleontological literature, there are so many erroneous explanations of recent mass mortalities that a critical review is desirable. It is obvious that an incorrect explanation of the cause of recent mortalities leads to a completely erroneous interpretation of mass mortalities in the geological past. Section II deals with the problems with which mass mortality has been connected in geological literature. While it is impossible to treat these problems in detail, the discussion may suffice to show that recent mass mortality occurs in regions where future deposits of geological importance (phosphorite, highly bituminous rocks) are developing. The numbers in this chapter refer to the detailed accounts of mass mortalities in the appendix. CATASTROPHE AND “ANASTROPHE” In the first half of the nineteenth century scientists searched for records of mass mortality in recent times to confirm Cuvier’s theory of catastrophes. By...