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where the adherence of the particles is loosest, the fluid, loaded 

 with suspended earthy particles, slowly collects, drop after drop, 

 and deposits its earthy matter in a stalactitic form; whilst, from 

 those parts, where the resistance to the admission of the fluid is 

 greater, the more closely filtrated fluid deposits only a coat of drusy 

 crystals. The examination of a polished section of one of these 

 crystalline geodes shows the opaque crust, in the closest continuity 

 with the transparent silicious mass ; the crust being more opaque, 

 as it extends to the circumference, and the internal crystals ac- 

 quiring a greater degree of pellucidness, as they reach towards the 

 centre. A similar gradual departure from opacity to clearness, 

 effected much in the same manner, may be observed in the familiar 

 instance of the crystallized mass, which sometimes forms on the 

 external surface of a flannel strainer, which has been employed for 

 the filtration of a saturated saline solution. This circumstance is 

 particularly observable in the fossil fruits of Mount Carmel, of 

 which we shall have again to speak more fully ; the external sub- 

 stance of these is generally of a light fawn colour, marked in some 

 parts by a dark ochrous tinge ; but the more internal part is white, 

 and is generally completely transparent toward the centre. These 

 bodies also, almost always, contain the above described internal 

 stalactiform projections, which are covered by a drusy crystalliza- 

 tion. In these crystalline, as well as in the other geodes, water is 

 frequently found, forming another species of the enhydros ; and 

 where it has not been found, very minute, and almost impercep- 

 tible, fissures or pores, may, during a long space of time, have 

 allowed the liquid gradually to escape. A careful examination of 

 these crystalline and agatine nodules, and long reflection on the 

 circumstances, of their formation, oblige me, in opposition to the 

 opinions of Dr. Hutton, and of Mr. Playfair, to believe, that they 

 must have derived their origin, from silicious matter in a, crystal- 

 line form, deposited from its solution, in a fluid menstruum, filtrat- 



