O'Reilly — On the Dates of Volcanic Eruptions. 397 



depths. However, there are not many observations available in this 

 regard ; in any case it is important to note that the most fearful and 

 most frequent eruptions of Iceland nearly all happened in summers 

 following remarkably mild winters ; that the most violent eruptions 

 of the Indian Archipelago follow immediately the rainy season or 

 take place during it ; that permanently active volcanoes show greatly 

 increased activity during this period, etc. Admitting the influence on 

 the development of volcanic activity of the penetration of meteoric 

 water, whether it be in the form of tropical rainfalls, or as molten 

 snow and glacier masses, we must also, at least, ascribe the same 

 influence to sea-water. 



"A wider and more important conclusion to be drawn from the 

 rapidity with which volcanic eruptions follow atmospheric changes, is 

 that the focus (" Heerd ") of volcanic activity is to be looked for at 

 much less depths than is usually admitted : an opinion which I 

 endeavour to sustain in my extended work, on numerous and various 

 ■grounds. I am led to admit that that focus is to be found for most 

 volcanoes at no greater depths than 30,000 to 40,000 feet under the 

 sea-level ; while for many it may be close under their very basis." 



It is thus quite evident that Kluge's Paper of 1862 refers simply 

 to his conclusion, that in high latitudes the eruptions take place 

 mainly in the summer months. There is no reference in the Paper to 

 the sun-spot period in this connexion. It is otherwise as regards his 

 ^'Treatise on Synchronism and Antagonism" referred to by Greikie 

 in the note on p. 72 of his text-book already refei'red to. It is in this 

 more extended work that he brings out the relation to be found 

 between volcanic eruptions find the sun-spot period ; and as, on the 

 one hand, it contains a great many important and valuable data with 

 reference to the question of vulcanism in general, and, as on the other, 

 that he puts his views in a very clear and precise manner, it may be 

 useful to give at least a summary of the more essential parts of the 

 work and of his conclusions. 



In the preface he says it is based on his greater work : this being 

 a complete catalogue of volcanic eruptions, dating back from the year 

 B.C. 1000 to the year a.d. 1863, and embracing 1450 such events. 



He requests that the conclusions at which he arrives will only 

 be considered as an attempt to present the complicated question of 

 volcanic phenomena in a simpler and clearer manner than that usually 

 accepted by geological science up to that time. 



He commences by the remark, that precisely, as formerly, great 

 eignificance was attached to the synchronism or periodic alternation 



