DALY. — THE NATURE OF VOLCANIC ACTION. 117 



the roof of a laccolith. The injection is of comparatively late date, 

 presumably Recent or Quaternary. *3 



We may now briefly note other probable examples of the opening of 

 vents above satellitic injections. Testimony to its existence in former 

 geological periods and in other regions tends to strengthen belief in 

 the hy])othesis as imagined in this Hawaiian study. 



Tertiary and OUer Vents from i>atellitic Injections. Suahian and 

 Scottish Examples. — As a result of his extraordinarily thorough study 

 of the mid-Miocene eruptions in Suabia, Branco concluded that the 

 Urach region is underlain by a " kuchenformige Masse," or laccolith. 

 In ground-plan its estimated diameters range between thirty and 

 forty-tive kilometers. Its position coincides with that of a very low, 

 but broad doming of the Jurassic strata in the Bavarian Alb, as 

 determined by Regelmann. Through secular erosion, the frontal 

 escarpment of the Alb has retreated at least twenty-three kilometers 

 since the volcanic epoch. 



On the top of the Alb plateau are thirty-eight tuff vents ; in the 

 escarpment are thirty-five more, and in the " Vorland," or region 

 traversed by the escarpment in its southward retreat, there are fifty- 

 four tutf vents and five basaltic vents. Xo lava flows occurred on the 

 Alb, and the few lava necks have become visible because of denudation 

 in the "Vorland." Though the explosion funnels are still more or less 

 intact on the Alb, the largest of them, the Randeck "Maar," does not 

 exceed one kilometer in diameter. The average diameter of the 132 

 vents is far less. The evidence is clear as to the short life of each of 

 these vent.s, which Branco has made the world type of "volcanic 

 embryos." Their brief, almost wholly explosive activities, their distri- 

 bution in a cluster without reference to master fractures, and the dome- 

 like warping of the Jurassic beds in this region, all declare the justice 

 of Branco's laccolithic hypothesis. Furthermore, his discussion of ^lan- 

 delsloh's 340-meter boring at Neuff'en shows that the temperature 

 gradient in at least one part of the Urach region is abnormally high, 

 about ten meters per degree Centigrade. Branco regards the abnor- 

 mal gradient as due to the wave of heat still being conducted from the 

 mid-Miocene injection. This suggestion is by no means extreme and 

 it clearly tends to support his laccolithic hj^iothesis."* (See also p. 100.) 



The peculiar abundance of small tuff-necks of Permian age in ])art3 

 of Scotland is subject to a similar tentative explanation. Various 

 memoirs of A. Geikie have made these vents famous as types of true 



" H. Reck, Moniitshcr. deut. rcoI. Gcs. No. 4, I'.tlO, p. 2!«. 

 " W. Hranco, Schwabcn's 12."^ Vulkim-Embrj'oncn, Stuttgart, 1894. Cf. 

 E. Sut-as, Du3 ^Vntlitz dcr Erdc, Bd. 3, 2tc Uiilfe, 1909, p. 055. 



