264 CARNEGIE INSTITUTION OF WASHINGTON. 



the arrangement of gradients, is abnormal. Usually the temperature 

 of a coastal plain is not the same as the temperature of the adjacent 

 sea bottom, so that a submergence or an emergence of a locality cre- 

 ates a disturbance of isogeotherms. Similarly, the creation of an ice- 

 sheet and its removal cause changes of the surface temperature and 

 derangements of the isogeotherms. Outside the regions of actual 

 Pleistocene glaciatiou there were Pleistocene changes of climate, by 

 which the isogeotherms must have been deranged. These changes 

 were probably greatest in high latitudes and less in low latitudes. 

 The resulting conditions to be satisfied in the selection of a site for 

 boring are : (i) That it shall have experienced no change in later 

 geologic periods from marine to land conditions, (2) that it shall not 

 hav^e been covered by Pleistocene glaciers, and (3) that it be in low 

 latitude rather than high. 



Relation to Volcanism. — The movements of lavas, their intrusion 

 among other rocks, and their extrusion at the surface effect great 

 changes in the distribution of subterranean heat, and create disturb- 

 ances in the regularity of isogeotherms which are very slowly effaced. 

 The resulting condition for the selection of a site is that it be not 

 near a locus of volcanism in an}^ of the later geologic periods. 



Relation to Diastrophism. — Orogenic disturbances, or those result- 

 ing in the flexure and faulting of rocks, not only stimulate subter- 

 ranean circulation, but produce local concentrations of heat as the 

 product of mechanical and chemical work. The thermal irregulari- 

 ties thus instituted disappear very slowly. The resulting condition 

 for the selection of a site is that it be in a region not subject to oro- 

 genic disturbance in any of the later geologic periods. 



THE SELECTION OF A LOCALITY. 



In the practical search for a locality suited for the proposed deep 

 boring it seemed proper to restrict attention to the territory of the 

 United States, and in the application of the criteria enumerated 

 above I soon reduced the field of inquiry to narrow limits. The 

 condition that the rock penetrated should be of uniform composition 

 and of massive character barred all regions occupied by sedimentary 

 formations, for these are everywhere more or less heterogeneous, 

 and in nearly all localities admit the passage of circulating waters. 

 The only large bodies of rock whose uniformity is reasonably 

 assured are plutonic, and attention was therefore limited to the large 

 batholiths. 



In the Cordilleran region most of the mountain ranges are young 

 and are unfitted for the purpose, both because the temperature di.s- 



