382 



Memorias de la Sooiedad Cientifioa 



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

 municated with by good wagon roads. 



Excepting the beautiful samples exhibited at several Ex- 

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

 the onyx marble of Jimulco has never been seriously exploi- 

 ted, in spite of great attention and interest shown by many 

 European and American Companies, dealers and private par- 

 ties, owing to lack of knowledge as to the conditions of deposits 

 for quarrying purposes, etc. by the present owner. Attention 

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

 homogoenity of blocks, exceptional size as exhibited, but also 

 for the varieties and wonderfully variegated colours, harmo- 

 nious tones, straight and contorted stripes or banding not 

 found in the onyx produced at other places in Mexico. 



The large deposits of onyx marble of Jimulco are in the 

 cretaceous limestones forming the mass of mountains there, 

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

 ring the end of Tertiary ages by circulant and disolvent wa- 

 ters. That is the most general of formation of the only greatest 

 valuable deposits of onyx in the world like those of 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 of crystallization, hardness, etc., varying only 

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

 oxides and impurities contained, on which depends color, 

 shade and nature of banding. 



The way followed 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 for onyx masses and gray for li- 

 mestones. The outcroppings are remains of the filled grottes, 

 partially destroyed by erosion. The thickness and form of the 

 croppings, apparently similar to the ore veins, are very vari'a- 



