352 MERRILL — DISINTEGRATION AND DECOMPOSITION OF DIABASE. 



Number 3 shows particles of feldspar, augite and mica fairl}'- well disag- 

 gregated, tliougli even here many of the granules are compound. Num- 

 ber 4 differs mainly in being finer and of a lighter color, while 5, of a 

 rich mahogany brown color, appears to the unaided eye to be composed 

 mainl}^ of mica scales. The microscope, however, shows it to contain 

 numerous l)adly stained but quite fresh feldspathic particles and cleav- 



Name. 



Diameter of particles. 



1. 



2. 



3. 



4. 



5. 



6. 



7. 



8. 



9. 

 10. 

 11. 



Gravel 



Fine gravel. . . . 

 Coarse sand. . . 

 ]\Iediuin sand. . 



Fine sand 



Very tine sand. 



Silt 



Fine silt. ...... 



Clav 



Loss at 110°.... 

 Itjnition 



Total 



Above 2. nnn. 

 2. -1. mm. 

 1. - .o mm. 



.5 - .25 mm. 



.25 - .1 mm. 



.1 - .05 nnn. 



.05 - .01 mm. 



.01 - .005 nun. 



.005- .0001 nnn. 



Per cent. 



42.3 

 20.66 

 12.72- 

 9.37 

 4.97 

 4.18 

 1.13 

 0.37 

 1.67 

 0.66 

 1.73 



99.76 



age flakes of augite. Nu!nl)er G, the particles of which lie between .1 and 

 .05 of a millinieter in diameter, shows also only minute flecks of mica 

 recognizalde macroscopically, but contains both feldsi)athic and augitic 

 particles like number 5, while 7 and 8 are deep ocherous brown silts, 

 ottering no distinctive features to tbc unaided eye, and 9 would i)ass for 

 a light l)rown ocher. The material analyzed as silt (columns 5, 6 and 7 

 below) is the equivalent of numbers 7, 8 and 9 of this series. 



Chemical Analyses and their Discussion. 



Tbe cliemical nature of the fresb aii<l dccouiposed rock is shown in 

 the accompanying table, the results being in nearly every case averages 

 obtained from two or more analyses. The " fresh '' material, ol)tained 

 from the interior of one of the boulders, is firm in texture, has a bright, 

 clean fracture and shows to the unaided eye no signs of decom])ositi()n. 

 When pulverized and treated with acid, however, it effervesces distinctly, 

 indicating the presence of free carbonates, which are also observable as 

 secondary calcite when thin sections are examined under the microscope. 

 Some of this calcite is evidently a deposit from infiltrated waters, being 

 derived from the surrounding decom[)osed material, while a portion re- 

 sults from the decomposition of tbe silicate minerals in i)lace. Aside 

 from a slight kaolinization of the feldspars and development of chlorite 



