INTRODUCTION O 



the climatic and solar changes in various geologic periods, Tertiary, 

 Pleistocene, Prehistoric, and Protohistoric. The methods and instru- 

 ments developed in this research give us an improved approach to 

 various types of geologic material besides fossil woods. Chief among 

 these are the clay layers of de Geer and Antevs, dealing with the 

 retreat of the ice-sheet, the andesite laminations of Udden in Texas, 

 and the stalagmite deposits of Allison. This geologic material, with 

 much more that will come to light, will not be included in the present 

 volume, but will be reserved for future discussion. 



One can see that in all this we are measuring the lapse of time by 

 means of a slow- geared clock within the trees. For this study the 

 name "dendro-chronology" has been suggested, or " tree-time." This 

 expression covers all the dating and historic problems referred to in 

 the following chapters, as well as the study of cyclic variations and 

 the distribution of climatic conditions. 



COOPERATION 



But with this development there is added need of information 

 from other sciences. The relationship of solar activity to weather 

 is a part of a rather specialized department of astronomical science 

 called astrophysics. There is help which one needs from that science, 

 but which one can not yet obtain; for example, the hourly variations 

 in the solar constant. One would like to know whether the relative 

 rate of rotation and the relative temperatures of different solar lati- 

 tudes vary in terms of the 11-year sunspot period. These questions 

 have to do with some of the theories proposed in attempting to explain 

 the sunspot periodicity. We do not know the cause of the 11-year 

 sunspot period. Here, then, is work for the astronomers. Climate 

 is a part of meteorology, and the data which we use are obtained 

 largely from the Weather Bureau. The observing stations are usually 

 located in cities, and therefore we can not get data from proper places 

 in the Sierra Nevada Mountains of California, where the giant sequoia 

 lives. Considering that this big tree gives us the longest uninterrupted 

 series of climatic effects whose dates are accurately known, which we 

 have so far obtained from any source, it must be greatly regretted 

 that we have no long modern records by which to interpret the writing 

 in those wonderful trees. So far as I am aware, only one attempt is 

 now being made to get complete records for the future.* 



From the botanists and ecologists we need to know the exact 

 time of ring formation, the ability of the tree to conserve moisture 

 against the day of drought, the soil-moisture gradients at different 

 months, the different action of the tree in putting on a different color 

 of wood in the spring and autumn growth. 



In dating problems, this study has developed another important 



*CoJ. John R. White, in Sequoia National Park. 



