JE. S. Dana — Petrography of the Sandwich Islands. 465 



Bishop says that they are " crusts and soft interiors of the same 

 formation (apparently flowing lava) found on Launiupoko hill, 3 

 miles S. of Lahaina. A precisely similar formation occupies the 

 front of Mt. Ball, 1\ miles above Lahaina. The crusts are 

 often rolled under the gray, soft material. Many crusts of gro- 

 tesque form lie about, from which the softer part has been 

 washed away. Many portions of the gray, soft mass are of 

 great thickness. Much building stone has been hewn from it. 

 It presents no appearances of being the result of any decay, 

 being compact and of uniform texture, except the hard crusts, 

 many of which are crumpled up as if in flowing, like pahoe- 

 hoe." 



One of the specimens (28) is a whitish gray compact rock, 

 whose surface is worn out into a series of deep holes between 

 projecting ridges nearly one inch in height. The texture, 

 though appearing closely compact at first sight, is seen by the 

 glass to be minutely porous, and the surface is speckled with 

 very small rusty spots. Under the microscope it is seen to 

 consist almost exclusively of plagioclase, here and there por- 

 phyritically developed ; there are also the remnants of a bright 

 green pleochroic mineral present in traces only and obviously 

 the original mineral whose disappearance has left the rusty 

 spots ; it seems to be hornblende. A little biotite is also pres- 

 ent. Iron is scattered through the mass rather sparingly in 

 minute grains ; no augite was noted. Another specimen 

 shows the transition from the firm rock to a soft chalky 

 condition powdering under the fingers. The section is very 

 like the other just described, though the feldspar is much 

 clouded and an occasional red crystal of chrysolite is noted. 



A third specimen (32) is a flake from a large bowlder (8x5 

 X 4 feet) found one mile S. W. of the summit of Mt. Ball. 

 Mr. Bishop remarks that, in the 

 eroded cliff, bowlders occur ce- 

 mented by mud, being ejectamenta 

 from Mt. Ball. The specimen is 

 finely schistose and so soft and 

 friable as to separate easily into 

 thin silvery scales, and by hand- 

 ling it is soon reduced to a fine 

 powder. Microscopic examination 

 shows it to be very nearly the same 

 in material with the others, but 

 having a distinctly fragmental 

 appearance. There is more chrysolite present in small broken 

 fragments of crystals; there is also a little brown biotite in 

 scales. The mass is made up of penetration twins of plagio- 

 clase according to the Carlsbad law mostly arranged parallel to 



