174 HENRY G. SMITH. 



Hunt (as quoted by Dana), also found that the Kaolinite from 

 the Chaudiere Falls, which was obtained from the sandstone of 

 the Quebec Group, where it fills seams or fissures, exfoliated in 

 white cauliflower-like shapes. 



Johnson and Blake (loc. cit.) also state that one of the speci- 

 mens they investigated, and which came from a cavity in a coal 

 seam at Summit Hill, Carbon Co., Pa., when ignited increased in 

 jbulk, and that the microscope shows this to be the result of the 

 exfoliation of the crystals due to the expulsion of the water. 



That this is the cause, is apparent from the appearance of the 

 •crystals after heating before the blowpipe. They do not fuse, and 

 although more rugged in appearance, the general laminated 

 •structure of the larger crystals remains fairly perfect. The one 

 great difference is, that they have become opaque, and that indi- 

 vidual plates are almost absent (Plate xxiii., fig. 2.) 



Descloizeaux in his " Mineralogy," states that the interior 

 ■structure is fibrous ; the plates of my mineral do not show fibrous 

 ; structure, but they show that besides the perfect basal cleavage, 

 {which has often been pointed out), two other cleavages, one 

 parallel to the face of the rhombic prism, the other parallel to 

 the brachypinakoicl (Plate xxiii., fig. 4). I think this is most 

 important, (I do not find that these other cleavages have been 

 previously noticed) and probably accounts for the manner in 

 which kaolin is formed, as by mechanical action the crystals 

 -would readily disintegrate, breaking along these cleavage planes. 

 ■That this is so appears from Mr. Collins's paper ; he states that he 

 ;has noticed in a large number of samples of china clay from 

 .different localities, that when the clay has been properly prepared 

 there is an entire absence of these scaly or flaky particles, but 

 that when the reverse is the case, that they are always present. 

 We know that the plasticity of kaolin depends on the fineness of 

 the material. 



Completely decomposed felspar has been stated by Dr. H. C. 

 •Sorby to break up into granules of kaolin from g oVo to 50I00 of 

 ,an inch diameter. Among these granules were some small needle- 



