14 Anniversary Address of the 



were deposited, yet there have been brief eras of convulsion 

 on a very grand scale, when the ordinary repose of nature 

 was violently interrupted in particular regions (as in the 

 Alps, for example) in a manner wholly different, in regard 

 to the magnitude of the effects produced, from any which we 

 have witnessed in historical times, or which ever occurred 

 formerly during the ordinary and normal state of the globe. 



That doctrines of this kind are popular, I am well aware ; 

 and if you desire to know how many modern writers have 

 declared in their favour, I refer you to the excellent work 

 which has just been published by one of our foreign mem- 

 bers, M. d'Archiac, on the "The History of the Progress of 

 Geology from the years 1834 to 1845." He has executed 

 conscientiously nearly half of the laborious and delicate task 

 assigned to him by the Geological Society of France, and has 

 given us a faithful digest of memoirs written in a variety of 

 languages and scattered through the Proceedings and Tran- 

 sactions of numerous scientific bodies, or the periodical 

 magazines and journals of almost every civilized country. A 

 geologist of practical experience in the field, as well as of 

 extensive erudition, was required to make a good classifi- 

 cation of such complex materials, and justly to appreciate 

 their relative value. In M. d'Archiac's pages every author 

 of merit has been allowed an impartial hearing, and the ex- 

 positor's own occasional criticisms are not obtruded too pro- 

 minently on the reader's attention ; when they are offered, 

 they are so judicious as to aid us materially in understand- 

 ing the faithful analysis he has given of the opinions of others. 

 In the concluding part of his chapter on " Le terrain mo- 

 derne," and when speaking of active volcanoes, and in other 

 places, he stoutly denies the adequacy of the causes which 

 have modified the earth's crust in historical times to produce 

 effects such as may enable us to explain geological monu- 

 ments. " We must have recourse," he says, " to other causes, 

 both organic and inorganic, of a more energetic and even 

 paroxysmal character."* 



On this subject I must make two preliminary remarks : 



* Archiac, Hist, des Progres, &c. tome i, pp. 209, 670. 



