DISTRIBUTION SWEDEN 609 



tuffs, and agglomerates, there are dull greenish fine-grained diabases, 

 chiefly porphyritic, and some quite slaggy. 



"One of the most conspicuous features iu some of these lavas is the occur- 

 rence of the same sack-like or pillow-shaped structure which has been already 

 referred to as so marked among the Areuig lavas of Scotland. . . . occa- 

 sionally interleaved with gray flinty mudstones, cherts, and red jaspers, which 

 are more particularly developed immediately above." ^^ 



Am3^gdaloidal diabases with j^iHow structure occur with fragmental 

 volcanics and intrusive igneous rocks for 12 miles near Slane and others 

 south of Drogheda, associated with radiolarian cherts of Lower Llandeilo 

 (Ordovician) age. 



SWEDEN 



Sundius^^ has described fully the pillowy structures that characterize 

 the basal greenstone of the Kiruna (pre-Cambrian ?) series of regionally 

 metamorphic volcanics and sedimentary rocks. The rounded massive 

 portions of the rock range from a few decimeters to more than half a 

 meter in diameter and are separated by dark hornblendic "schlieren/' 

 with whitish streaks of scapolite, the whole resembling an agglomerate. 

 It is not sedimentary, however, but formed, according to the author, "by 

 the crowding of viscous lava bodies (pillows)." Common features are 

 radial jointing and a concentric structure consisting of a glassy outside 

 crust, bands of vesicles, and sometimes of variolites and differently colored 

 layers. The longest axes are parallel to the "surfaces of deposition," and 

 in some places there is a concentration of vesicles on the upper side of the 

 pillows. 



The characteristic skeleton crystals, microlites, and dark pigment of 

 the original glassy coatings of the pillows are well preserved, although 

 largely replaced by scapolite, which has also been extensively developed 

 by regional metamorphism in other rocks of the district of very different 

 composition. There is also much schistosity developed in places. Horn- 

 blende amygdules occupy vesicles elongated at right angles to the surfaces 

 of the pillows. 



"As a conclusion from evidence found in the field and under the microscope 

 it appears that the occurrence of the pillows must be considered a flow- 

 phenomenon in the lavas, where each pillow has formed an individual with 

 its own surface of cooling. At Pahtosvaara the pillows occur everywhere in 

 the fine grained varieties of the soda-greenstones, and when I have been able 

 to distinguish separate lava flows they appear along one of the surfaces or, in 

 one case, throughout the whole thickness of the bed." 



"^ A. Geikie : Ancient Volcanoes of Great Britain. London, 1807, pp. 239-244. 

 ^' N. Sundius : Pillow lava from the Kiruna District. Geol. Foren. 1 Stockholm 

 FOrhdl., vol. 34, 1912, pp. 317-333. 



