200 



EOCK DISINTEGEATION AND DECOMPOSITION 



forms a gray-brown sand composed of feldspathic particles^ 

 dirty brown augites, and lustrous scales of brown mica. Num- 

 bers 5 and 6 seemed composed almost wholly of beautifully 

 lustrous, dark mahogany-brown mica scales, while 7 would pass 

 for a finely micaceous umber. Numbers 8 and 9 were uni- 

 formly ochreous and without appreciable grit. 



Analyses of Fresh and Disintegrated Diabase from Medford 





Fresh Diabase 



BlSINTEGKATED 

 DlABABB 



Silt from Drs integrated 

 Diabase, Nos. 7, 8 and 9 









OF Table, on P, 199. 





I 



II 



III 



IV 



V 



VI 



VII 



CoHSTrrtrttKTft 





















°1^ 



aft 



eS 



P a « 



-•3 . 



CD O ff 



.. . t-^ TO 



° CQ i^ 



:2 o* 



CO ^ Q 







A 



«> l5 ,^ 



q 



S '3 "d 



•2 tf '2 



« +* oS 







■< 



l.^§ 



< 



^^§ 



OQ rt fl 



>» <U OS 



■a ?i <— 1 







^ 



l§g 



*0 



n o2 



fl §32 





3 



o 





w 



<t-Jw 



M 



<^ C w 



•<l PiW 



^ p..a 



B 



SiOg .... 



% 



47.28 



0/ 



/o 

 44.44 



/o 



/o 



% 



13.51 



% 



36.61 



f Sol. in HCl . 

 t Sol. in NoaCog 





1.19 





0.85 



0.47 









9,66 





8,65 



22.63 







AI2O3 .... 



20.22 



4.74 



23.19 



4.86 



21.98 



1 





FegOs .... 

 FeO ... . 



3.66 

 8.89 



]• 10.91 



12.70 



10.00 



12.83 



^ 5.88 



40.68 



CaO . . . . 



7.09 



3.09 



6.03 



1.50 



3.32 



0.12 



3.44 



MgO . . . , 



3.17 



2.20 



2.82 



1.84 



3.23 



0.79 



4.02 



MnO .... 



0.77 



Not det. 



0.52 



Not det. 



Not det. 



Not det. 



Not det. 



Kfi . 



2.16 



1.21 



1.75 



0.68 



1.30 



0.52 



1.82 



NagO .... 



3.94 



0.50 



3.93 



0.17 



0.90 



1.24 



2.14 



P2O5 .... 



0.68 



Not det. 



0.70 



Not det. 



Not det. 



Not det. 



... 



Ignition . 



2.73 



2.73 



3.73 



3.73 



10.86 



0.11 



10.97 





100.59 



36.23 



99.81 



32.2^8 



77.52 



22.17 



99.68 



The chemical nature of the fresh and decomposed rock is 

 shown in the accompanying table, the results being in nearly 

 every case averages obtained from two or more analyses. 

 The * 'fresh" material, obtained 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 decomposition. "When pul- 

 verized and treated with acid, however, it effervesces distinctly, 



