596 J. V. LEWIS ORIGIN OF PILLOW LAVAS 



of Saxony. He observed fathom-large masses of the rock separated from 

 one another by irregular fissures — some narrow, som*e wide^ — and these 

 filled with minute fragments of the same rock. Such structures, he 

 thought, could not well be exclusively the work of rushing torrents, and 

 the supposed conglomerate was believed to have had its boulders ground 

 together by earth movements in which it had been involved. In 1871 

 Naumann^ distinguished between the basal conglomerate of the Culm 

 and a supposed greenstone breccia, but considered both to have been pro- 

 duced contemporaneously by brecciation in situ. Credner^ concurred in 

 this conclusion. 



Rothpletz^ recognized the "Grundconglomerat" of the Culm as a true 

 conglomerate, but saw in its squeezed and faulted pebbles evidence of the 

 force to which he attributed the origin of the supposed breccia in the ac- 

 companying greenstone. In other words, he concluded that the remark- 

 able spheroidal structure of the greenstone was due to the action of intense 

 orographic pressure on a rock that had previously been broken by a system 

 of joints, so that movement took place throughout the mass, causing a 

 rounding and partial brecciation by the grinding of the joint -blocks on 

 one another. The rock is described as a dense, finely vesicular diabase, 

 and the ellipsoidal masses attain maximum dimensions of 0.3 meter for 

 the shorter and 1 meter for the longer axes. 



Dathe^ observed that these dark-green amygdaloids are variolitic, and 

 that the oval to egg-shaped masses of which they are composed are some- 

 what uneven on their surfaces and fit into each other. Hence he con- 

 cluded that they were formed contemporaneously from the magma. He 

 also found that the spheroids form layers that are approximately hori- 

 zontal and occur throughout the whole thickness of the flow, being espe- 

 cially well developed at the bottom. Many of the broken masses showed 

 a linear structure parallel to the outer surfaces, and in some of them the 

 varioles are arranged in concentric layers. Dathe also called attention to 

 the wide distribution of this structure in other parts of Yogtland, in the 

 Upper Devonian of the Lobenstein-Saalburg region, and in the Fich- 

 telsrebirge. 



The concentric arrangement of the amygdules parallel to the surfaces 



5 Erlant. d. ffeogn. Karte der TTmgegend von Hainichen im Konigr. Sachsen, 1871, p. 11. 



6 G. R. Credner : Das Griinschiefersystem von Hainicben im Konigr. Sachsen. Zeitschr, 

 fiir die gesammten Naturwiss., vol. xiii, 1876, pp. 117-245. 



■^ A. Rothpletz : Ueber mechanische GesteinsTimwandlnneen bei Hainichen in Sachsen. 

 Zeitschr. d. deutschen geol. Gesell., xxxi. 1879, pn. 855-898. "Die Brecclenbildung des 

 Aktinolithschiefers oder sogen. Griinschiefers von Hainichen," pp. 874-398. See also 

 Erlaut. zur geol. Specialkarte d. Konigr. Sachsen, Sec. Frankenberg-Hainichen, 1881, 

 p. 16. 



8 E. Dathe : Beitrag zur Kentniss der Diabas-Mandelsteine. Jahrb. d. Konigl, Preuss. 

 geol, Landesanstalt u, Bergakad. Berlin, 1888, pp. 410-448, 



