Mr. D. Mushet on the Cryslaliization of Iron. 83 



lustre, highly shining and metallic : yields to the knife. Spe- 

 cific gravity 4*6 — '^'9. 



No. 9. 4-0 feet. Pudding-stone and sandy breccias, of a 

 dark-brown colour ; composed of very small siliceous pebbles 

 cemented together. There are frequently slender white veins 

 passing thi'ough the masses of stone several feet in length. 



No. 10. 20 feet. About twenty feet only is visible of this 

 stratum, which consists of very dark pudding-stone; in some 

 places being almost black. Large rounded blocks are scat- 

 tered about the beach, and are only discernible at low water. 



No parallel layers of flints are observable in any jiart of 

 this section of the chalk strata ; but some occur of great size 

 in the chalk-pits at Thornham and other adjoining parishes, 

 of the description which have obtained the name of Paiamou- 

 drce. These were of a cup-like shape, three or lour feet long, 

 and ten or twelve feet round, resembling those at Whitiling- 

 ham and Thorpe near Norwich. 



I am yours, &c. 



Norwich, Jan. 17, 1823. RiCHARD Taylor. 



XXI. On the Crystallization of Iron. By Mr. David Mushet. 



[Continued from p. 24.] 

 npHE crystallization of cast-iron may be divided into twp 

 •^ classes; namely, that which takes place in chasms or shrink^ 

 ages of die metal, and that which is merely superficial. The 

 former possesses the greatest beauty and variety, and may 

 with propriety be divided into three distinct stages. 



1st. That in which crystallization may be said to have coni- 

 menced, and which, while confined to this stage, may truly be 

 called linear. This is indicated by a series of lines running 

 parallel or concentric to each other, according as the chasm 

 inclines to a plane or hemisphere. These ground iiiies are 

 intersected at right angles by a slighter class of lijies, which 

 has the effect of covering the surface of the meti,il with a che- 

 quered series of dots and minute hollow squares. 



This stage ol" the operation takes place when a small chasm 

 is formed by shrinkage of a ))roportional quantity of fluid iron. 

 Its beauty and regularity will greatly dei)end upon the process 

 being eflijcted in die absence of external air; wherever air has 

 reached the surface of the iron, the sharpness of the lines, and 

 a still more minute and silvery ground-work crystallization, 

 are destroyed by oxidation, and the beauty of the specimen 

 very much impaired. 



L 2 Tlic 



