42 GEOLOGICAL REPORT. [172 



brown, very extensively employed), and may be rendered undis- 

 tinguishable from the latter by a very slight admixture of lamp 

 black. — Burning does not change the hue of the paint, but alters 

 the dull red of the raw material to a brick red, which would also, 

 of course, be the color of vessels made of it. The mass docs not fuse 

 readily, but is quite refractory ; a very high temperature deepens 

 its color and finally blackens it, with the appearance of incipient 

 fusion. 



72. As for the manner in which this deposit was formed, the white spots 

 mentioned, between which and the red mass there is a zone of gradual transition, 

 seem to prove that the whole was originally white, and was subsequently 

 impregnated with a ferruginous solution. Unlike the other white ciay 

 deposits mentioned, this material, notwithstanding its compactness, is found on 

 close examination to contain numerous minute pores, which in the white portions 

 are distinctly marked by the ferruginous lining of their walls, though equally 

 existing, and open, in both the white and the red portions of the bed. Under 

 the lens they appear distinctly angular, and the space has evidently at some time 

 been occupied by crystals of the form of a square, or possibly rhombic, prism 

 or plate — (probably the former ; the length of the major axis being about 0.02, 

 that of the minor 0.01 of an inch), the substance of which has in most cases 

 almost entirely disappeared ; although in a few instances I have found those in 

 the white portions incrusted inside with (yellow) hydrated peroxide of iron ; 

 while that in the red mass is evidently anhydrous. 



Whatsoever may have been the original substance of these crystals, it is 

 manifest that the red color did not spread from them as centers (as might be 

 supposed had they been iron pyrites), inasmuch as the latter is entirely indepen- 

 dent of them in its outlines. Their substance was evidently removed by a 

 lixiviating process before the coloring solution infiltrated the clay. — In the lignitic 

 formations, we find clays in which minute crystals of iron pyrites are thus 

 disseminated throughout the mass, and the circumstance that all the pores in the 

 white mass possess an inner coating of iron rust, seems to confirm the supposi- 

 tion that their origin is to be sought in crystals of pyrites, the form of which may 

 have been either that of distorted cubes, or more probably, of the rhombic 

 prisms of magnetic pyrites.* 



*I may mention in connection with the metamorphis of iron pyrites, just 

 quoted, another singularly complicated case, occurring at McDouglas' milL 

 Tishomingo county (1[87). In a loose bed of hornstone pebbles, overlying the 

 lower cretaceous clay, and itself overlaid by Orange Sand, we find some pebbles, 

 studded with little druses of brown iron ore, a few of which still exhibit the forms 

 of a regular octahedron. Similar pebbles, studded with (mostly tetrahedral) crys- 

 tals of pyrites, occur at Turner's mill (1T83) ; and there can belittle doubt that 

 here, the common transformation of pyrites into brown iron ore has occurred. 

 But in the interstices between the pebbles, we find loose masses, also of brown 



