552 REPORT OF NATIONAL MUSEUM, 1893. 



described. The cave marbles vary even more irregularly, both in extent 

 and quality. The deposit may be a mere veneering over the face of the 

 rock, and although there is apparently an abundance, judging from 

 appearances alone, the actual amount of available stone may be 

 extremely small.* Moreover, such deposits are rarely uniform tor any 

 great distance, either in texture or color. Owing to coarse crystalli- 

 zation, they fracture easily, and, moreover, are more than likely to con- 

 tain numerous cavities, large and small, known popularly as " thumb 

 holes" and "i)iu. holes." The small amounts of metallic oxides and 

 organi-c matter they contain render the colors light and usually dull. 

 White, yellowish, amber, and reddish, with a resinous luster, are com- 

 mon. The rock as a rule is less translucent than the true onyx marbles, 

 and when polished appears "muddy" and unsatisfactory. Neverthe- 

 less, such deposits do not infrequently yield comparatively small blocks 

 of beautiful material and material that is doubly desirable because it 

 is unique. 



Properly managed such can be worked up to good advantage, but too 

 much has been expected from them, and it is this fact that ha^s led to 

 the disastrous failures following every attempt that has thus far been 

 made to work the cave marbles in America. If the material as taken 

 from the ledge could be assorted by some competent person and worked 

 up, each block for such a purpose of ornamentation as it seemed best 

 adapted, then we might hope for some interesting results. But at best 

 the cave marbles of America must rank as "uniques" rather than 

 objects of commercial value. They will never become regular sources 

 of supply. There is too much waste and too much uncertainty regard- 

 ing amount and quality. 



A marked and very beautiful feature of the onyx marbles in gen- 

 eral, and particularly of those which originate as spring deposits, is 

 the fine, undulating, parallel bands of growth or lines of accretion 

 shown on a cross section, and which are of course due to its mode of 

 origin through successive depositions upon the surface (see pi. 1). The 

 stone owes its chief value for decorative purposes to its translucency, 

 fine veination, and color. In many instances the original hues have 

 become enhanced by oxidation and through the development of retic- 

 ulating veins of small size, due to incipient fracture, into which perco- 

 lating waters have introduced new coloring solutions or locally oxidized 

 the protoxide carbonates, which seem to form tlie chief coloriug constit- 

 uent, as already noted. 



The localities from which the finer grades of stone oi tnis type have 

 in times past or jjreseut been obtained are few and widely scattered, 



* The writer has met with just sucli cases iu his experience. A certain deposit 

 was represented as a solid mass of inercliautable stone, showing a (juarry face 100 

 or more feet in length by some 20 or 30 feet in height. On inspection it was 

 shown that the "quarry face" was but a thin coating of stalactitic matter over 

 the sloping wall of an old cavern. Not a cubic yard of merchantable stone ctiuld 

 have been obtained in the entire outcrop. 



