598 J. V. LEWIS ORIGIX OF PILLOW LAVAS 



Oder solchen, welche zusammengesetzt sind aus geflossenen Tropfen, Zapfen, 

 Spharoiden, gewundenen, abgenindeten Gestalten, wie man sie an den erkalte- 

 ten Lavastromen der nach tatigen Vulkane so oft sieht." 



Denckmann and Streng^* observed at Herborn and Londorf similar 

 pbenomena, including rounded and elongated rolls and ropy forms, which 

 they regarded as marking the cooling surfaces of lava, and Brauns^'' has 

 described analogous structures in the Upper Devonian diabases at Quot- 

 shausen and Homertshausen, in the Hessian hinterland. At the former 

 an exposed surface showed rope-like and fluted lava, with rounded (wulst- 

 artig) masses, the surfaces of which are coated with glass; at the latter 

 locality the upper surface of one flow and the bottom of another that im- 

 mediately overlies it are also glassy and characterized by thick, rounded, 

 and saeklike masses. Heineck^® found ^'dickwulstige, runde Formen, die 

 sich als Oberflachformen erweisen'^ in the diabase flows about Herborn. 



Brauns^" calls attention to the wide-spread occurrence of well preserved 

 '^'stream-surface'' j)henomena in the '"Deckdiabas" of uppermost Devonian, 

 which consist of rounded swells and large and small spheroids closely 

 packed together and attached to the massive rock by short, thick necks. 

 The crusts are glass, with a variolitic layer beneath it in some places, and 

 the masses have a radial, spokelike jointing. The plates illustrating this 

 article show typical pillow lava, both in surface features and in cross- 

 sections. 



Reuning^- found along the newly constructed road from Herborn to 

 Dreidorf that the structures heretofore called '"flow," "'surface," and 

 "'cooling'' forms, such as characterize the upper surfaces of many modern 

 flows, in reality constitute the whole thickness of many of the flows, and 

 that many of the rounded, spheroidal, ellipsoidal, and roll-like masses, 

 which appear at first glance to be entirely isolated individuals, are con- 

 nected to each other by short, little necks. The diameters range up to 

 more than a meter : all are coated with glass, and radial, spokelike joint- 

 ing is common. The filling between the masses is chiefly granular calcite 

 in some beds, more chloritic in others, and at one place (near Xeumhhle ) 

 large spheroids are embedded in a light gray limestone that is rich in 



" A. Denckmann and A. Streng : Zeitsehr. d. deurschen geol. Gesell.. vol. 39. 1S87, pp. 

 624. 625. 



*3 R. Brauns : Mineralien und Gesteine au-? dem hessichen Hinterland. 2^itschr. d. 

 deutschen geol. Gesell.. vol. 41, 1889. pp. 491-544. 



" Fr. Heineck : Die Dialja.se an der Balinstrecke Hirtenrod-Uebernthal bei Herborn. 

 Neues Jahrb. Min.. etc.. B. B., vol. xvii. 1903. pp. 77-162. 



" R. Brauns : Def Oberdevonische Deckdiabas. Diabasbomben. Schalstein. und Eisenerz. 

 Xeues Jahrb. Min.. etc.. B. B.. vol. xxi. 1906. pp. 302-323. 



^ Ernst Reuning : Diabasgesteine an der Westerwaldbahn Herbom-Dreidorf . Neues 

 Jahrb. Min., etc.. B. B., vol. xxiv, 1907, pp. 390-459. 



