BUILDING AND ORNAMENTAL STONES. 433 



Accordiuj^ to Ziikcl, the ;ivt!ray,o clicinicitl (;()iiii)().situ)ii of diabasi; is 

 as follows : 



I'cr ociit. 



Silica 40. T)! 



Alumina 11.0.') 



Iron protoxide 1 1. 27 



Lime 8. Ml) 



Magnesia .^>. 28 



Potash 1.10 



Soda :5.H8 



Water 2.2;» 



Average specific gravity, 2.8, eciiial to a weiglit of ITo pounds jtcr 

 cubic foot. 



lu classification two principal varieties of diabase are reiiogiiized, the 

 distinction being founded ui^on the iireseuce or absence of tbe mineral 

 olivine. We thus have (1) olivine diabase, or diabase with olivine, and 

 (2) diabase proper, or diabase without olivine. 



Owing to its lack of definite rift, comi^act texture, and hardness, dia- 

 base can, as a rule, be worked only with difficulty and usually at a cost 

 considerably greater than that of granite. It is therefore not exten- 

 sively quarried, though of late years it has come into more general use 

 for paving puri)Oses, and still more recently for buUding and manu- 

 mental work. Tlie green aniique porphyry or Marmor Jjacedmmonium 

 viridc, formerly much used foi' ])avements and general inlaid decorative 

 work in (Ireece and Kome, is, according to Belesse,* a diabase consisting 

 of large greenish crystals of labradorite embedded in a fine compact 

 ground mass of the Sfime feldsjtar, together with augiteand titanifcrous 

 iron.' The (juarries from which the stone was taken aie stated by IluHt 

 to be situated between Sparta and Marathon, in (Jreece. A stone of a 

 similar character and closely resembling it in color and structure is 

 abundant among the drift bowlders of eastern Massachusetts, but its 

 exact derivation is unknown. 



In the eastern United States the dikes of diabase are frequently as- 

 so(;iated with deposits of red or brown Triassic sandstoiu?, whi(;h are also 

 extensively quarried, as will be noticed j'urther on. Concerning these 

 dikes Professor Dana writes: | 



"It is remarkable that these fractures (through which llu' dial)ase 

 was forced to the surface) should have taken place in great numbers 

 just where the Triassic beds exist, and only s[)aringly east or west of 

 them ; and also that the igneous rock should be essentially the sam(», 

 throughout the thousands of miles from Nova Scotia to North Carolina. 

 The igneous and aqueous rocks (sandstone) are so associated that tlicy 

 necessarily come into the same history. Mount Tom and Moiml llol 

 yoke, of INlassachusetts, are examples of these tiaj) ridges; aisn I'^ast 

 Kock and West Ifock, near New ilaven, and the Hanging Hills, near 



*Annal8 de Mines, p. 25(i. 

 tO/). ('if., p. 73. 



t Manual of Geology, third cdilioii, p. 417. 

 IT. Mis. 170, ])t. 2 28 



