356 MR. HELGI PJETURSSON ON A SHELLY [Aug. I903, 



27. On a Shelly Boulder-Clay in the so-called ' Palagonite- 

 Formation ' of Iceland. By Helgi Pjetursson, Cand. Sci. Nat. 

 (Communicated by Prof. W. W. Watts, M.A., Sec.G.S. Head 

 April 29th, 1903.) 



It is a fact well worthy of note that, while the basalt- formation of 

 Iceland bears, geologically, a very close resemblance to the basalt- 

 plateaux of the British Isles, the Tertiary volcanic phenomena of 

 this latter region present nothing strictly analogous to the great 

 tuff- and breccia- or so-called ' palagonite-formation ' of Iceland. 

 For it is obvious that the fragmental materials of the British vol- 

 canic region, which are intercalated with the basaltic lavas and only 

 of ' trifling thickness,' l cannot have their geological equivalent in 

 the great palagonite-formation of Iceland, which covers thousands 

 of square miles, and in isolated patches is met with over a greater 

 part of the total area of the island. 



The palagonite-formation has been in several respects a puzzle 

 to the geologists who have visited Iceland : some have been of the 

 opinion that the tuffs and breccias are contemporaneous with the 

 plateau-basalts or even older ; but the more systematic investigations 

 of Prof. Th. Thoroddscn have shown that in reality the fragmental 

 masses arc younger than the basalt-formation. 2 Prof. Thoroddsen 

 thinks that towards the close of Tertiary time the central parts of 

 Iceland were buried under a continuous covering of fragmental 

 volcanic materials 3000 to 4000 feet thick, which formation was 

 broken up into single mountain-masses and isolated fells before and 

 during the Glacial Period. 3 



In the summer of 1899 it was observed that very considerable 

 masses of ground-moraine are intercalated with the breccias which 

 constitute hills rising out of, or bordering, the southern lowlands of 

 Iceland 4 ; and in subsequent years observations in distant parts of 

 the country brought out the same general result, namely, that there 

 exist in Iceland extensive traces of intense glacial action, older than 

 those known to geologists before 1899, and that we are fully justi- 

 fied in speaking of a ' Glacial palagonite-formation.' 5 



The breccia-formation of the peninsula of Snaefellsnes, which I 

 investigated in the summer of 1902, like that of other parts of the 



1 Sir Archibald Geikie : ' The Ancient Volcanoes of Great Britain ' vol. ii 

 (1897) p. 194. 



2 See. for instance, Prof. Thoroddsen's ' Vulkaner i det nordostlige Island,' 

 Bih. t. K. Svensk. Vet.-Akad. Handl. vol. xiv, pt. ii (1888), no. 5, p. 68. 



3 Thoroddsen, Dansk. Geograf. Tidsskr. 1898, p. 2 (sep. cop.). 



4 Helgi Pjetursson : ' The Glacial Palagonite-Formation of Iceland ' Scot. 

 Geogr. Mag. vol. xvi (1900) pp. 265-93 ; & ' Nyjungar i Jardfradi Islands 

 Eimreidin ' 1900, pp. 52-57 (Icelandic). 



5 Helgi Pjetursson : ' Moramer i den island ske Palagonitformation,' Overs. 

 Kgl. Danske Vidensk. Selsk. Forhandl. 1901, pp. 147-71; & ' Fortsatte 

 Bidrag til Kundskab om Islands " glaciale Palagonitformation " ' Geol. Foren. i 

 Stockholm Forhandl. vol. xxiv (1902) pp. 357-69. This last paper embodied a 

 few observations made during the summer of 1901. 



