144 UNIVERSITY OF MISSOURI BULLETIN 



foundation of a structure. We have not traveled far enough 

 yet to determine the direction in which we are going. 



For example, our knowledge of Pre-Cambrian geological 

 history is practically a blank. This blank interval is probably 

 as long as the whole of the time that has elapsed since Cam- 

 brian times. Yet of this entire interval our real knowledge 

 of the general order of its events can be stated in a few sen- 

 tences. Not only do we not know its history, we have not yet 

 discovered a sure means of interpreting its record. We are 

 able to read local records for short periods of time and for 

 small isolated localities, but we do not know how to correlate 

 them. Before any great progress can be made in this field 

 we must discover some way to interpret its record that will 

 be as serviceable as the organic remains have been for Cam- 

 brian and later geological history, or as the study of land 

 form has been for the interpretation of the history of land 

 areas. 



Similarly, we are yet unable to explain the great changes 

 of climate that have taken place in the past. We know by 

 abundant evidence that the same locality has repeatedly suf- 

 fered changes from glacial cold through tropical heat and 

 moisture to desert desiccation. We know that some of the 

 geological periods were periods during which desert condi- 

 tions obtained over great areas of the earth, and in others 

 tropical conditions extended into the realm of existing glacial 

 regions, such as Greenland. Whether these changes are ter- 

 restrial or cosmical we cannot yet definitely say, though there 

 is good evidence in existence that many of them have been 

 terrestrial or even continental and, therefore, fit subjects for 

 geological investigation. 



Up to the present time geologists have found no means 

 of making an accurate estimate of geological time. Under the 

 principle of uniformitarianism several attempts have been 

 made, based on the existing rate of geological change. The 

 results have differed so widely when worked out by different 



