MODE X. IRON-STONE. ,97 



STRUCTURE II. COLUMNAR. 



Mr. Sowerby possesses in his valuable museum 

 a curious example of this kind, being quadrangular 

 columns of iron-stone passing through slate. 



STRUCTURE III. VARIEGATED. 



This kind, with an appearance of shells, &c. 

 has been already mentioned. 



The rock upon which the Capitol of Rome was 

 founded, is thus described by Breislak. 1. The 

 colour is brick red, but with spots of a deeper 

 tinge, and which are also of a larger grain. 2. Its 

 hardness surpasses that of tufa, but is inferior to 

 that of lava, being comparable with that of the 

 freestone used at Paris. 3. If large pieces be 

 broken off with the hammer, the fracture is even 

 conchoidal ; in small the fracture is unequal, small 

 grained, but never rough. 4. It acts on the mag- 

 netic needle at the distance of two or three lines. 

 5. It contains scales of mica, fragments of felspar, 

 and white globules of calcareous spar, with some 

 fragments of melanite. 6. Observed in the sun 

 with a good lens, the whole mass is found to be 

 crystallised. 



If this rock be not a red basalt, it may pass 



VOL. I. H 



