162 



MR. W. S. BOULTON ON THE 



I.May 1904, 



eighth to one-sixteenth of an inch across, are very numerous, often 

 with the typical concave surfaces, due to fracture across vesicles. 

 In among these lapilli, calcite-crystals occur, and round their borders 

 is a brown, yellow, or red ring of iron-oxide derived from the basalt- 

 fragments, while fringing some lapilli arc clusters of small, pale- 

 yellow rhombs of dolomite, showing patches of bright yellow and 

 borders of red iron-oxide by reflected light. 



V. Some Special Characters of the Basalt-Sheet. 



The characters of this igneous flow which are of especial interest 

 are (a) the ; pillowy ' structure, together with the tuffy or agglome- 

 rate structure; and (A) the included lumps and masses of limestone. 



Pig. 2. — Oval, slaggy lumps of basalt-lava surrounded by 



fluxion-tuff. 



1 Foot 



Pig. 3. — Lump of basalt-lava, enclosing a lump of tuff and of lime, 

 stone, and itself enclosed in coarse fluxion-agglomerate. 



AG.G. TUFF 



( 



LIMEST. 



1 Foot 



The pillowy, oval, or spheroidal masses of basalt, 2 to 

 8 feet across, usually very amygclaloidal, especially round their 

 periphery, and sometimes containing small oval or angular cores of 

 a slightly different and earlier lava, are usually embedded in a tuff 

 made up of lapilli up to 2 or 3 inches across (figs. 2 & 3). 



