In a recent paper (Cook, 1951) the fossilization of bone was consideredfrom the standpoint of the behavior of the principal components: calcium,phosphate, and carbonate. These substances may increase or decrease with theduration of fossilization and in detail are subject to wide fluctuation,depending on the chemical nature of the soil matrix in which the bones are imbedded.Leaching, accumulation, and ion exchange may raise or lower the levelof any of the inorganic constituents in such a way as to make the analyticalvalues in a single specimen of little use in estimating the age of the bone.The organic matter, on the other hand, appears to undergo a consistent secularreduction which is much less dependent upon the chemical and physical environment.The water content likewise decreases quite uniformly with age.The present paper reports the results of recent investigations of theorganic components and water in fossil bone. Application of the results todating is not attempted here in detail but will be dealt with in a separatepaper.

The main controlling factor of physical conditions and processes,and of distribution and spread of plants and animals, is climate and itschanges. Low temperature and, in some regions, excessive snowfall havecaused extensive glaciations. The withdrawal of water to form the icesheets lowered the oceans. Increased precipitation and reduced evaporationinduced pluviations in arid regions. Rise of temperature has madeice sheets and glaciers shrink and disappear. Climate has thus controlledthe geological factors. Biota have moved latitudinally andaltitudinally with the climatic belts. Plants and animals have beentrapped by climatic changes in unfavorable locations to become regionally.or universally extinct.The temperature rise which has occurred during the last hundredyears in North America and in Europe (and perhaps elsewhere), togetherwith the general parallelism of the past temperature histories, indicatethat the marked, long-continued temperature ages have prevailed simultaneouslyin the two continents. The major temperature ages and theirsequences consequently supply a basis for long-distance correlation; andthe temperature changes should therefore be used for the principaldivision of time. Regionally, subordinate divisions on other conditionsmay be practical. In dry and semiarid regions the natural basis isconditions and changes in moisture. For stratigraphic divisions erosionsare suitable markers.