546 EEPORT OF NATIONAL MUSEUM, 1893. 



assumed their present state, and that the alabaster was deposited when their temper- 

 ature was higher, and when, perhaps, they were beneath deep waters. However, 

 this opinion is little better than conjecture." 



Bischoff,* iu discussiug similar phenomena, says: 



"It is interesting to know that mineral springs can deposit granular limestone. I 

 dou])t whether hot springs are V)etter suited to this than cold, from which the depo- 

 sition takes place slower than from the former ; but the slower the CaCOt is deposited, 

 the more likely is it to assume a crystalline form. " 



J. L. Smith, writing- of the thermal waters of Hierapolis, says:t 



"The amount of water is very great, and it is so highly charged with carbonate of 

 jimeasto incrust all bodies that it comes in contact with, and it takes place sorajjidly 

 that the coucretion does not possess great solidity, and frequently has a granular 

 form, resembling driven snow." 



W. H. Weed, in writing on the deposition of calcareous matter by 

 the waters of the hot springs of the Yellowstone National Park,says:t 



"Another variety * " * is that which forms the lining of hot-spring ventholes. 

 This is deposited comparatively slowly, and occurs in shelly layers half au inch to 

 3 inches thick, with a smooth, rounded, and globular surface. It is crystalline and 

 marble-like and pure white. This travertine is a crystallization out of a supersatur- 

 ated solution of carbonate of lime, due to the relief of pressure as the waters 

 approach the surface. A similar deposit lines the ventholes of the Orange and other 

 springs, and is analogous to the deposit so quickly formed in the conduit pipes 

 leading the hot water to the hotel baths, also due to supersaturation, experiments 

 showing that such solutions do not deposit their excess of lime at once, but in the 

 coiirse of a short time." 



Bearing iu mind that these onyx marbles are of calcite, and so com- 

 pact as to acquire under proper manipulation an enamel-like i)olish, 

 and fitrtber that, as noted later, they are all superficial deposits, it re- 

 mains to formulate our own opinions regarding their origin and to note 

 Low far they differ, if at all, from those above given. It is well to 

 note, at the very outset, that while there is no apparent doubt but that, 

 with the exception of the deposits in caves (see p. 550), the onyx marbles 

 are the result of spring- action, I have been able to learn of no single 

 instance in which material of this nature is now forming, the recent 

 deposits invariably taking- a tufaceous structure. It is singular, to say 

 the least, that widespread phenomena due to purely local causes should 

 be so nearly synchronous in action and that we should be living in an 

 age of cellular deposition only. 



It is evident that, so far as their mineralogical nature is concerned, 

 the onyx nuirbles may be products of deposition from water of any 

 ordinary temperature, hot or cold. Accepting the fact that such depo- 

 sition would take i)lace more slowly from a cold than from a hot solu- 

 tion, and that the more slowlj' deposition takes place the more likely is 



* Chemical and Physical Geology, Vol. 1, ]>. 152. 

 t Original Researches, p. 64. 



t Formation of Travertine and Siliceous Sinter by the Vegetation of Hot Springs. 

 Kinth Ann. Rep., U. S. Geological Survey, 1887-'88. 



