190a-191U.I 2QQ 



and (2) fixed dendrites. In the former class he included such 

 crystalline arborescent growths as native copper, silver, gold, tin, 

 and lead, and the minute dendritic and plumose crystalites found 

 in the acid lava called pitchstone. The simplest form of a free 

 dendrite was a snow-flake. The chlorite in moss-agate was also 

 an example of free dendritic growth, as it was originally a free 

 crystalline growth and subsequently determined the contour of 

 the chalcedonic layers deposited around it. Fixed dendrites on 

 the other hand were formed invariably after the substance in 

 which they were found, and their form was to a great extent 

 modified by the peculiarities of the latter. In mocha-stones, for 

 example, the dendritic oxide of manganese entered the stone 

 in solution through accidental cracks and thereafter the growth 

 was limited to the minute interstices between the layers of the 

 chalcedony. Similarly dendrites in flints, found commonly on 

 the hills around Belfast, were limited to cracks and to the porous 

 cortex of the stone. Dendrites were also common in limestone 

 and other porous rocks. They also occurred in cracks in crystals 

 and between the lamince of mica. 



Closely allied in structure to dendritic oxide of manganese 

 were the dendrites of ice which adorned our windows in frosty 

 weather. Dendrites were also found in paper where they were 

 produced by the slow oxidation of particles of bronze derived from 

 the paper-making machinery. These dendrites of copper oxide 

 were at one time mistaken for fungoid growths, and until lately 

 many erroneous ideas were current concerning them. After nearly 

 seven years observation of them, the lecturer said he had been 

 enabled to solve many of the problems connected with dendritic 

 growths in paper, and his views on the subject had been brought 

 before the Royal Microscopical Society and published in their 

 Journal about two years ago. 



In conclusion Mr. Strachan described some pseudo-dendritic 

 growths which had no crystalline structure and then gave a 

 detailed explanation of the phenomena which gave rise to 



