382 Memorias de la Sociedad Científica 



from la Noria Station M. C. R. R. in open valleys and com- 

 municated with by good wagón roads. 



Excepting the beautiful samples exhibited at several Ex- 

 hibitions, principally at París and San Antonio, Tex., last year, 

 the onyx marble o£ Jimulco has never been seriously exploi- 

 ted, in spite o£ great attention and interest shown by many 

 European and Amerícan Companies, dealers and prívate par- 

 tías, owing to lack o£ knowledge as to the conditions o£ deposits 

 £or quarrying purposes, etc. by the present owner. Attention 

 was attracted to this onyx not only on account.of its hardness, 

 honiogoenity o£ blocks, exceptional size as exhibited, but also 

 £or the varieties and wonder£ully variegated colours, harmo- 

 nious tones, straight and contorted stripes or banding not 

 found in the onyx produced at other places in México. 



The large deposits o£ onyx marble o£ Jimulco are in the 

 cretaceous limestones £orming the mass o£ mountains there, 

 in which the onyx filled caves or grottes in the limestone du- 

 ring the end o£ Tertiary ages by circulant and disolvent wa- 

 ters. That is the most general o£ £ormation o£ the only greatest 

 valuable deposits o£ onyx in the world like those o£ the Uni- 

 ted States, Algeria and Italy. The concretionary masses of 

 onyx fill entirely the cavities and give in all parts the same 

 texture grade o£ crystaüization, hardness, etc., varying only 

 in every point in the intensity of color on the average o£ iron 

 oxides and impurities contained, on which depends color, 

 shade and nature o£ banding.; 



The way £ollowed by nature in the formation of onyx gi- 

 ves an idea by which we can appreciate the formation of such 

 deposits. So I see on the surface long and broad outcrop- 

 pings or irregular, large patches easily recognized on the field 

 by contrast of color, whitish f or onyx masses and gray f or li- 

 mestones. The outcroppings are remains of the filled grottes, 

 partially destroyed by erosión. The thickness and form of thé 

 croppings, apparently similar to the ore veins, are very varia^ 



