2ck> HISTORY OF GEOLOGY AND PALEONTOLOGY. 



were made by Hochstetter, Suess, and Reyer on molten 

 sulphur and other substances which absorb gases in large 

 quantities, and during the process of cooling from the molten 

 condition, the escape of the gases was accompanied by 

 explosive phenomena. Under certain circumstances, at the 

 places of explosion conical-shaped masses formed resembling 

 those of volcanic mountains. 



F. Earthquakes. Earthquakes may arise in the solid crust 

 or in still deeper horizons of the earth. They accompany all 

 the more violent eruptions, but they may take place quite 

 independently of volcanic phenomena. Records of earth- 

 quakes have been handed down from the earliest times, but 

 the classical and mediaeval writers confined themselves to the 

 descriptions of the leading natural phenomena, and the 

 catastrophes and terrifying effects produced by earthquakes on 

 people and animals. 1 



Scientific research of earth-tremors may be said to have com- 

 menced in the beginning of the eighteenth century, and had 

 already progressed so far that Hoff was able to compile an ex- 

 cellent monograph of earthquakes for the second volume of 

 his work. Another good account of the phenomena and 

 effects of earthquakes was published in Friedrich Hoffmann's 

 posthumous works (1828). An essay by Dr. Kries upon the 

 origin of earthquakes was awarded a prize at Leipzig in 1827. 

 Naumann's Text-book of Geognosy contained a complete 

 resume of all the scientific facts about earthquakes known 

 before 1850. So exhaustive was Naumann's account that 

 Landgrebe could bring forward little additional knowledge 

 in his Naturgeschichte der Vulkane und Erdbeben (vol. ii., 



1854)- 



All the earlier writings of the nineteenth century follow 

 Alexander von Humboldt in representing earthquakes and vol- 

 canoes as different manifestations of the same set of causes. 

 Humboldt defined earthquakes as "Reactions of the earth's 

 nucleus against the solid crust," and volcanoes as " Safety- 

 valves" for the immediate neighbourhood of such disturbances. 

 Emil Kluge, who made a special study of the earth-tremors 

 and shocks in the years 1850-57, supported Humboldt's 



1 A short historical account of the prevailing views regarding earth- 

 quakes which were held by the authorities of antiquity and the Middle 

 Ages, will be found in R. Hoernes' Erdbclenkunde, Leipzig, 1893. 



