328 REACTION OF THE INTERIOR OF THE EARTH 



to Boss, a deep caldera, having an encircling ridge with 

 a strongly detonating solfatara, from which have radiated 

 streams of lava flowing into the sea, and now forming 

 small promontories ; this island furnished volcanic mill- 

 stones in the time of Strabo. (Boss, Reisen auf den Griech. 

 Inseln, Bd. ii. S. 69 and 72-78.) For the British Islands 

 I may here refer, on account of their antiquity, to the 

 remarkable effects of submarine volcanoes on the Lower 

 Silurian strata (Llandilo flags), inasmuch as volcanic 

 cellular fragments are imbedded in these strata ; and, 

 according to Sir Roderick Murchison's important obser- 

 vation, eruptive masses of trap even penetrate into the 

 Lower Silurian strata in the Corndon Hills (Shrop- 

 shire and Montgomeryshire) ( 468 ) ; the dyke phenomena 

 of the island of Arran ; and other places where there is 

 evidence of the introgression of volcanic activity, but no 

 traces of actual volcanoes have been found. 



2. Islands in the Atlantic. 



Volcano Esk on the island of Jan Mayen, ascended 

 by the meritorious Scoresby, and named by him after 

 his ship ; height rather less than 1600 feet. An open 

 but not burning summit crater ; basalt, rich in pyroxene 

 and trass. 



South-west of the Esk volcano, near the north cape 

 of Egg Island, another volcano, which, in April 1818, 

 ejected ashes to a considerable height, at intervals of 

 four months. 



Beerenberg, 6872 feet high, in the broad north-eastern 

 part of Jan Mayen, (71 4' N. lat.) is not known to be a 

 volcano. ( 469 ) 



