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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 crystallization. 
In these crystalline, as well as in the other geodes, water is fre- 
quently found, forming another species of the enhydros ; and where 
it has not been found, very minute, and almost imperceptible, 
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 cir- 
cumstances, 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 crystalline 
form, deposited from its solution, in a fluid menstruum, filtrating 
