'H't'2 The American Geologist. April, 1894 
on mure careful study to be replacements. As more <>r less probable 
examples I may cite the celebrated Cave mine of Beaver county, I tali : 
some of the lead and zinc deposits of the Mississippi valley (enlarged 
<;ash veins); and a series of small caves near < >uray, < tolorado, in quartz- 
ite overlain by shales and containing native gold. 
(h) Brecciated cavern veins, rilling collapsed or breccia ted beds result- 
ing from solution, dolomitization, or some other chemical change. This 
type is related to the last very much as the shear veins arc to the true 
fissure veins. Particular strata of limestone arc weakened by tin- solv- 
ent action of percolating , water, they collapse and become brecciated, 
and between and around the fragments thus resulting the vein minerals 
are deposited. It is obvious thai metasomatic replacements might not 
be readily distinguished from deposits of this type. Among the actual 
occurrences supposed to belong here are the specular hematite of 
Crawfprd county, Mo. : the copper ore of St. Genevieve. Mo.; the lead 
and zinc deposits of the upper Mississippi valley (in part), including 
the lower flats and tumblers of Chamberlin; and the zinc deposits of 
southwestern Missouri. 
2. Impregnations, or deposits filling- the pores and often 
replacing the original or normal constituents of various rocks 
(metasomatosis). — Although second only, in importance, to 
veins, this main type of aqueous deposits maybe more briefly 
described. Certain t} T pes of impregnations occur chiefly, as 
already explained, in the walls of veins, the fissure having af- 
forded a passage for the impregnating solutions in each case. 
Also, impregnations, like veins, may or may not occur along- 
igneous contacts. In the subdivisions of impregnations we 
nniy properly distinguish the concretionary, pore-filling but 
not concretionary, and metasomatic but not concretionary; 
types, as follows : 
(ai Concretionary deposits that an not metasomatic — impun concretions, 
due to the segregation of a soluble constituent in a siliceous or other- 
wise insoluble rock. The segregating minerals are chiefly carbonates 
(calcite, etc.) and the carbonate or other soluble salts of iron from which 
the iron is often deposited as the insoluble oxides. Being unable to re- 
move the siliceous matrix, the segregating minerals are deposited in it. 
more perfectlj cementing the particles of clay, grains of sand, etc. The 
common claystone is a familiar example of these impure concretions — 
combinations of concretion and mat rix; and clay ironstone may he named 
as the child' economic example. 
ib) Concretionary deposits that art metasomatic— pure concretions, due to 
the segregation of a soluble constituent in a soluble or metasomatically 
replaceable matrix. The siliceous concretions of calcareous rock (Hint 
and chert nodules, geodes, etc.) are clearly the most important exam- 
ples, and no more distinctly economic examples have occurred tome; 
