TJncrystallized Mineral Substances. B59 



this case, the fineness of the matter, the elegance and regularity of the 

 form, would appear, in equal circumstances, to be increased in a remark- 

 able manner. 



Besides observations on the form and a microscopic analysis of these 

 bodies, I have made experiments with precipitates and the residuum of 

 a great variety of substances, and have taken particular care to examine 

 the forms of the calcareous precipitates under the microscope. The fol- 

 lowing are the principal results of my inquiries. 



I could not succeed, either on a former occasion or at the present, in 

 imitating the true corpuscles of the chalk, but only produced something 

 bearing some resemblance to them. These precipitates of carbonate of 

 lime presented forms of very great variety. 



The microscope enabled me, in general, to perceive solid concretions, 

 under three principal forms. 



First, In the form of an indeterminate, homogeneous, vitreous mass. 

 This structure appeared like an irregular and rapid aggregation of very 

 minute particles of matter, pretty equal among themselves. 



Secondly, As corpuscles regularly conformable, which derived their 

 shape from very minute particles of matter, round in appearance, ap- 

 proaching each other in different degrees of development, and seemingly 

 subjected to an internal central force of attraction or formation. Thii is 

 the most common appearance presented by the precipitates or combina- 

 tions of the most varied description. 1 have found these corpuscles to 

 be in every respect analogous to the large morpholites spoken of above. 

 In a flake or nebulosity, at first very slight, we see simple spheres formed 

 of fine grains, double spheres, kidneys, double kidneys, articulated rods, 

 granular rings, and lastly bodies which run into each other, and resemble 

 a bramble-berry. The four first are simple forms, the rest have always 

 presented a higher degree of development, not appearing as simple struc- 

 tures but highly composite. These various scries of forms are what I name 

 Morpholites or Crystalloids. They result from an internal force which dis- 

 poses the material particles in a certain order without producing any 

 change upon them. 



Thirdly, In forms having the character of a structure with parallel 

 faces, such as that which distinguishes crystals. This mode of structure, 

 however, appears from observation to be rarely primary, but rather se- 

 condary. The first example occurs when the regulating force has inter- 

 fered, often also when it has ceased to act. Occasionally this struc- 

 ture proceeds with incredible activity; sometimes it advances slowly. 

 The intervention of the force of crystallisation causes the grains to disap- 

 pear. It is a chemical process of transformation. Never have I seen a 

 crystal forming itself of visible material corpuscles, but almost always by 

 a wonderful and sudden transformation of small morpholites or crystal- 

 loids into either simple or composite crystals, according as the former were 

 cither simple or in groups. These sudden transformations have formerly 

 been noticed by other observers, but under different relations, and anion"- 

 other?, ia the chloro-arsciiiatc of lead, which, from being at first in grains 



