PALAGONITE OF SELJADALR 121 



I can conceive how, the small cavities being filled by a fluid (super- 

 heated steam?) of different kind from the surrounding magma, the 

 quartz can have been in part carried by osmosis through the film of 

 glass which bordered the cavity and separated the two diverse fluids to 

 form the pure radiate quartz, while the remaining portions of the quartz 

 and calcite were compelled to solidify in the surrounding magma, in 

 which needles, and even large crystals of the normal anhydrous con- 

 stituents of the diabase, were forming in every direction. In this way 

 all the variants of the quartz-albite ground were produced. 



The Palagonite of Seljadalr 



My mind goes back thirty-five years to the old house beside the labo- 

 ratory of the Hofrath Wohler, in Gottingen, where that fine scholar, 

 Professor Wolfgang Sartorius von Waltershausen, lectured on miner- 

 alogy. I remember the detail with which he discussed the minerals of 

 the Binnenthal and the theory of the feldspars, the series going up to 

 krablite 1 : 3 : 24, and including the amorphous hydrated feldspars of 

 the palagonite group. I little imagined then that a third of a century 

 later I should find palagonite almost in sight of my own college at Am- 

 herst and mix it up with sideromelan, but such was to be the case. The 

 memory of those ancient lectures is not so clear as the memory of the 

 genial peculiarities of the good teacher. So when I found a curious 

 glass scattered in small portions in a peculiar facies of the Holyoke trap 

 I turned to Rosenbusch* who describes and figures the palagonite of 

 Seljadalr as the type of an "Aschentuff," wherein the darker grains with 

 pitchy luster are the original lapilli, which he identifies with the nearly 

 anhydrous sideromelan of von Waltershausen, while the lighter colored 

 intervening bands are the very hydrous products of a secondary chemical 

 decomposition, and form the " dull and earthy " cement of the clastic 

 fragments. It was further stated that while this peculiar tuff was exten- 

 sively developed in every part of the world the palagonite was found 

 nowhere except in this clastic form. I remembered that von Walter- 

 shausen connected the peculiar changes through which he believed the 

 mass to have passed with a submarine deposition, and as the develop- 

 ment of the glass in the case I was studying was connected with the 

 unusual introduction of water into the mass I began to search for any 

 description of a similar glass in situ, and soon I began to come on dis- 

 crepancies. As my glass was soft, friable, and easily soluble in weak 

 acid, I had connected it with the palagonites immediately, and as it was 

 let black and very fresh I had called it sideromelan, supposing it to be 



♦Gesteinslehre, p. 319; Mic. Phy., ii, 1896, p. 1040. 



