Results of Geology. 67 



pressure evenly exerted with the finger (or spring clothespins) 

 will force out all unnecessary balsam, and leave the section and the 

 protecting cover perfectly flat and unbroken. 



The reader will not deem me too prolix when he attempts his 

 first preparation, or when, after having followed the plans so 

 scantily given in the books, he feels the need of something pre- 

 cisely definite. Ifc is certain that neither Canada balsam nor 

 gum mastic will retain the first ground side of a specimen upon 

 a slide long enough to enable the preparer to reduce it to the 

 requisite thinness, and with both these substances heat must be 

 employed, which is objectionable because most objects are there- 

 by warped or cracked ; and furthermore the paper guard, which 

 I hold to be indispensable for limiting and equalizing the thinness 

 of a section, is not mentioned in treatises, in which, if known to 

 the author, such a measure should be noticed. But it is possible 

 to fasten agate, fossil wood, &o with hot gum shellac, so that they 

 may be ground upon both sides with a water stone ; but even in 

 these instances invidious cracks may endanger or destroy the beau- 

 ty of a choice preparation. 



I am confident that my specimens are second to none in any 

 respect: and the highly creditable performances of friends, to 

 whom I have given the method forming the subject of this com- 

 munication, lead me to' believe that with the facilities it affords 

 the observers of our country will need no Topping for objects 

 within their reach, and I beg leave to add that the profitable 

 pleasure I have enjoyed induces me, through the American Jour- 

 nal of Science, to invite participation. 



ARTICLE IX. — General Position and Results of Geology. 

 (From the Anniversary Address of the President of the Geo- 

 logical Society of London, 1857.) 



Let me now close my address by a few observations necessarily 

 occurring to my mind, as the result of these investigations. First, 

 then, it appears to me, we are steadily progressing towards a 

 knowledge of the material structure of the crust of the earth, and 

 of the modifications it has undergone in the long course of ages ; 

 and such a knowledge seems essential to the right appreciation of 

 many of the phenomena connected with the variations in the fauna 

 and flora of the surface of the earth. In regard to the natural 

 history of the earth, every day produces new genera and new 



