Vol.54.] 



ON THE BALA & OTHEK ROCKS OF LAMSAT. 



137 



porcelainized, while the 

 igneous rock becomes much 

 more finely granular. 



The corals, chiefly Favosites 

 sp., "which are found in the 

 limestone are not obliterated 

 by the alteration in it, but 

 are to be seen to within an 

 inch or two of the igneous 

 rock. From this limestone 

 we also obtained Halysites 

 catenularia, Linn. 



The limestone is covered 

 by a conglomerate formed of 

 large and small blocks, the 

 larger of which sometimes 

 reach 6 feet in diameter and 

 are usually rounded, while the 

 smaller blocks are frequently 

 angular. 



The matrix is sometimes 

 calcareous and contains small, 

 perfectly - preserved corals, 

 but is more usually a black 

 shale in which small angular 

 fragments of rocks are irregu- 

 larly scattered, so that it 

 resembles an ash in appear- 

 ance. The included blocks 

 are usually of limestone, very 

 often fossiliferous (Favosites 

 sp., Halysites catenularia, 

 Linn., Heliolites megastoma, 

 M*Coy ?, and Rafinesquina 

 expansa^ Sow., small var., 

 having been obtained), and 

 of andesite ; but blocks of 

 black earthy shale, green 

 slate, grit, conglomerate, cal- 

 careous ash, and coarse por- 

 phyrite also occur. 



A section of this rock 

 showed fragments of various 

 andesites, one a rock formed 

 of parallel acicular felspars 

 in a much altered matrix, 

 another a fresh mica-andesite, 

 a third a vesicular andesite, 

 all embedded in a matrix 

 formed of fragments of crys- 

 tals, quartz, and iron-ores. 



W 







W. 



e» 





< 5 



tL 2 





$Q 



o 



tci 







^ 



55 



