1 888.] NEW-YORK MICROSCOPICAL SOCIETY. 139 



THE MICROSCOPICAL INVESTIGATION OF ROCKS. 

 A PLEA FOR THE STUDY OF PETROLOGY. 



BY DR. H. HENSOLDT. 



{Delivered April 20th, 1 8 8 8 . ) 

 Mr. President, Ladies and Gentlemen : — 



It is not without reluctance that I have accepted the invitation 

 to deliver this address, because the subject is not altogether, a 

 popular one. I have often wondered why there are so few in 

 the ever increasing army of microscopists, who take an interest 

 in the microscopical investigation of minerals and rocks, and 

 why there are fewer still, who have selected this department as 

 their special field of study. 



Of course I am aware that this army is mainly composed of 

 amateurs. They do not lack the ability, but, in nine cases out 

 of ten, they have not the time necessary for thorough and 

 methodical work. Yet among these very amateurs we find a 

 large number of enthusiastic workers, who, in spite of all draw- 

 backs, accomplish wonderful things, make original discoveries, 

 and lead the way to entirely new fields of microscopical 

 research. 



Now it may be doubted whether within the whole range of 

 practical microscopy there is a subject which so well repays 

 study — a subject so eminently calculated to afford pleasure and 

 satisfaction to the lover of the microscope as the investigation 

 of the minute structure of minerals and rocks. It is question- 

 able whether the whole field of zoology and botany, in fact the 

 entire organic division of nature can present to the inquirer 

 a greater complexity of forms, a more wonderful display of 

 colors, a more startling array of problems — problems strange 

 and fascinating in their mystery — than this neglected world of 

 stones. 



Here we have a field as yet almost untrodden, and affording 

 endless opportunities for research to an army of workers. We 

 all know what the proboscis of the blow-fly looks like. When 

 we are about to examine it under the microscope we know 

 exactly what to expect — we have seen it before, and could 



