76 Intelligence and Miscellaneous Articles, 



mate resemblance between the gypsum of the lagoons and the ab- 

 normal gypsum beds of secondary regions. 



If the silicification of the Macigno which we have noticed in the 

 neighbourhood of the solfatara of Pereta should appear an exag- 

 gerated application of the theory brought forward, the verification 

 of it may be traced in the lagoons of Sasso, where the solution of 

 the si lex of the freestone and its redeposition are manifest in all 

 places where circumstances allow of this double transformation. The 

 Fumacci of Sasso rise, to the south of the establishments, from be- 

 neath a vast mantle of fine-grained freestone, over which passes the 

 mountain road connecting the valley of the Cornia with the Province 

 of Sienna. At intervals the road is interrupted by isolated boiling 

 pools or shallow cavities, which exert a metamorphic action upon 

 the region which they traverse. The first evidence of alteration is 

 apparent in the colour of the rock, which from blackish-gray becomes 

 white. It is cracked in all directions. The vapours follow quickly 

 these lines of separation, attack the silica of the macigno, dissolving 

 it out, and immediately depositing it under a gelatinous form. The 

 gelatinous mass becomes opake in the air and assumes the resin-like 

 appearance peculiar to hydrated silica. In connexion with this we 

 observe imbedded in a siliceous cement, nuclei of a white micaceous 

 sandstone unaltered at the centre, causing a breccia appearance. This 

 kind of breccia is finally, by the complete solution of the nuclei, 

 converted into a grayish rock entirely siliceous, which resounds under 

 the hammer like clink- stone, and resembles exactly by its aspect and 

 its roughness of touch, porcelain biscuit, Sometimes the solution is 

 more rapid, and then the rock is formed of an agglutination of little 

 grains analogous to those of an ancient quartz rock and possessing its 

 tenacity and hardness. Examined with a glass, each grain is composed 

 of an independent particle or driblet of hydrated silica, and they 

 seem to have collected as viscous tears, such as would have adhered 

 together in hardening. Breislak observed at the solfatara of Poz- 

 zuoli fragments of decomposed lava bound together by a siliceous 

 substance almost vitreous ; but in the lagoon of Sasso the solution 

 and permanent regeneration of silica, effected at the expense of the 

 macigno, are carried on upon a vast scale and over a space of great 

 extent. — Bull. Soc. Geol. cle France, Dec, 1848, 147 ; and Silliman's 

 American Journal of Science for May, 1850. 



ON THE INTERPRETATION OF MARIOTTE'S LAW. BY LIEUT. 

 E. B. HUNT, U.S. CORPS OF ENGINEERS. 



It is readily demonstrated that in any entirely homogeneous me- 

 dium, the component parts of which act on each other by forces va- 

 rying as any function of the distance, Mariotte's law must prevail. 

 Both elastic tension and cohesive force will necessarily vary as the 

 density, in a medium assumed as homogeneous, quite irrespective of 

 the law of force, the variation being expressed in terms of distance 

 between the component parts of the medium. Whether the force 

 be attractive or repulsive, varying inversely with the first or hun- 

 dredth power of the distance, the result is the same ; that entire 

 homogeneousness makes Mariotte's law necessary. 



