286 CARNEGIE INSTITUTION 



at various depths. Rock specimens from the core should be exam- 

 ined in the laboratory to determine their heat difFusivity, and this 

 should be investigated (i) in relation, to varying pressure, and (2) in 

 relation to varying temperature. 



The results to be hoped from such an investigation are : 



1. A deteitninatiou of the general temperature gradient of the 

 upper part of the crust — a determination having higher authority 

 than any previously made. 



2. A detenmnation of the downward variation of temperature 

 gradient. 



3. A redetermination of the rate at which heat reaches the surface 

 through conduction in the crust. 



4. A determination of any variation in the rate of heat movement 

 in relation to depth. The character of such determined variation, 

 or the determination of the absence of variation, bears on theories 

 as to the source of the heat conducted toward the surface. 



5. The detection of variations of gradient occasioned by Pleisto- 

 cene oscillations of climate, and their possible interpretation in terms 

 of time. 



The value of such a research will depend largely upon the depth 

 penetrated b}'- the boring. I am informed by Mr. F. H. Newell, of 

 the United States Geological Survey, that core drilling has hereto- 

 fore been carried only to moderate depth, so that for the purposes 

 of such an investigation a special plant, of an elaborate character, 

 will be required. This plant should provide for the commencement 

 of the boring with a large diameter and fhe progressive reduction of 

 diameter as greater depths are reached. The plant should be care- 

 fully planned in advance, and such planning requires expert knowl- 

 edge and skill. Mr. Newell informs me that the necessary knowledge 

 and skill can be commanded, and mentions in that connection Pro- 

 fessor Slichter, of Madison, Wisconsin. 



I am not prepared to make recommendation as to persons by v/hom 

 the proposed investigation should be conducted ; but if the Institu- 

 tion shall establish a laboratory of geophysics the general direction 

 of the investigation might advantageously be entrusted to the ofl&cers 

 of that laboratory. 



I estimate that the amount of money needed for the work \\dll be 

 $50,000, that the time probably covered would be three j^ears, and 

 that the need for the first year would be $10,000. 

 Very respectfully, 



G. K. Gilbert. 



