ADDRESS TO THE HELVETIC SOCIETY. 263 



various works on fishes, radiates, and mol- 

 lusks, a new chapter of nature was all the 

 while unfolding itself in his fertile brain. 

 When the Helvetic Association assembled at 

 Neuchatel in the following summer, the young 

 president, from whom the members had ex- 

 pected to hear new tidings of fossil fishes, 

 startled them by the presentation of a glacial 

 theory, in which the local erratic phenomena 

 of the Swiss valleys assumed a cosmic sig- 

 nificance. It is worthy of remark here that 

 the first large outlines in which Agassiz, when 

 a young man, planned his intellectual work 

 gave the key-note to all that followed. As 

 the generalizations on which all his future 

 zoological researches were based, are sketched 

 in the Preface to his " Poissons Fossiles," so 

 his opening address to the Helvetic Society 

 in 1837 unfolds the glacial period as a whole, 

 much as he saw it at the close of his life, af- 

 ter he had studied the phenomena on three 

 continents. In this address he announced his 

 conviction that a great ice-period, due to a tem- 

 porary oscillation of the temperature of the 

 globe, had covered the surface of the earth 

 with a sheet of ice, extending at least from 

 the north pole to Central Europe and Asia. 

 " Siberian winter," he says, " established itself 



