ANNIVERSAKY ADDRESS OF THE PRESIDENT. IxXXV 



markable, inasmuch as it does not occur in the older rocks, which 

 are generally persistent for great distances and throughout their 

 whole thickness, except in the case of the conglomerates. 



Amongst the special phenomena which the author describes in 

 this formation, may be mentioned the great inclination of the upper 

 limestone beds in certain localities, also that the disturbances in 

 the stratification of the zone of claj^s and gypsum are milch more 

 distinct than in the upper zone of limestone ; they present nume- 

 rous undulations more or less abrupt in their stratification. On the 

 left bank of the Jarama are the soda-mines of Protectora, 4 or 5 

 kilometres east of Crempozuelos ; the beds are horizontal and con- 

 sist of clays and gypsum. The sulphates of soda and of soda and 

 lime which are worked, occur chiefly in the clays extending through 

 a thickness of about 15 metres ; they occur either in detached 

 masses in cracks and hollows, or disseminated throughout the whole 

 mass. One of these cracks is very remarkable, having an undulating 

 course in a more or less horizontal direction. Other local distur- 

 bances and unconformabilities of the diff'erent strata are described; 

 they are probably owing to some agitation of the waters of the lake 

 during the process of deposition. The origin of these rocks is 

 attributed to mechanical or chemical causes, and sometimes to a 

 combination of the two. The origin of the gypsum appears to the 

 author more involved in difficulty. Was it derived from springs of 

 water which held it in solution, or was it the result of metamorphic 

 action ? The gypsum of Madrid is found in beds and in the crys- 

 talline form of selenite. Masses of both kinds occur also in the 

 argillaceous beds ; sometimes only loose plates of selenite occiu', at 

 others it occurs in veins either single or intersecting each other, and 

 in many other forms. The saccharoid gypsum or alabaster is scarce 

 in this province, but it abounds in the neighbouring province of Gua- 

 dalajara, where it forms large masses or nodules, which are enveloped 

 in a red argillaceous covering or coat*. 



The formation of silex and resinite was also probably owing to 

 springs containing it in solution. The emission of silex during this 

 period must have been enormous, for almost all the Tertiary lime- 

 stones contain it in large proportions, as much as 20, 30, or 40 per 

 cent. Magnesia and salts of soda are also abundant ; but rock-salt 

 does not exist in this province, although it is found in the neigh- 

 bouring province of Toledo, on the south side of the Tagus, and in 

 the district of the Ebro at Remolinos, province of Zaragoza. Here 

 the beds of rock-salt are of great thickness, it being, as the author 

 observes, a remarkable fact that this substance, originally derived 

 from the sea (?), should occur so abundantly in a freshwater forma- 

 tion. 



The author next describes in detail the different minerals found 

 in this formation, many of which are interesting, and might be made 

 of great commercial importance ; they are quartz, flint or^silex, resi- 

 nite (both opal and hyalite), nitre, salt, sulphate of soda, thenardite, 



* See Description of Nodules of Alabaster in the Mines of Castellana in Tus- 

 cany, by W. J. H. Quart. Journ. Geol. Soc. vol. i. p. 282. 



