GO 



PROCEEDINGS OF THE CHICAGO MEETING 



the chloroform. Leave over night in a tightly stoppered bottle, In a warm 

 bath at a temperature of about fifty degrees centigrade. For a number of 

 successive days gradually add powdered Canada balsam, from which all the 

 turjpentine has previously been driven by heat. This process should be con- 

 tinued for a week, and when the balsam has become as concentrated as possi- 

 ble, at a temperature of sixty or seventy degrees centigrade, the bottle is then 

 immersed in a bath of water at the boiling point, so as to drive off all the 

 chloroform. This will take a day or two. Finally the material is kept in a 

 bath of glycerine (in the bottles, of course), kept at such a temperature as to 

 keep the balsam melted and slightly bubbling. A very low Bunsen flame is 

 enough, since the glycerine stores up heat and readily overheats and burns the 

 balsam — a result to be avoided. About ten hours in the glycerine bath are 

 enough. The pieces are then pulled out of the fluid balsam and allowed to 

 cool, when they are ready for grinding. 



Figukl; 2. — SccUon of Clay, Wooilsi lUe, JS'ew Hampshire 



To grind specimens of unconsolidated fine material prepared in this way, 

 considerable care must be taken, when the desired thinness is approached, not 

 to disrupt the section. They are not quite as firm as rock specimens. With 

 care and patience good sections may be made by one used to grinding rock 

 sections, although a novice might fail. Another difiiculty is in avoiding grind- 

 ing marks. Such difliculties as these, however, should not discourage any one, 

 for many good sections have already been made with a minimum of practice. 



Cut number 1 is a section of seasonally deposited clay from Woodsville, 

 New Hampshire. The top of the winter layer may be seen at the bottom of 

 the picture. Note the abrupt change from winter to summer conditions, as 

 shown in the sizes of the grains. This clay Is extremely fine. The long parti- 

 cles are laths of sericite. The magnification is 250 diameters. 



