New Forms of Concretions — Nichols. 

 Connecticut River 



53 



Hartford, Connecticut. 

 Deerfield, Massachusetts. 



South Hadley, Massachusetts. 

 Charleston, New Hampshire. 



Cumberland, Maine. 



Broad Cove, Maine. 



805-1 



55-1 



76-3 



805-3 

 75-2 

 76-1 



Vo-3 

 805-9 



75i 



753-2 



753-J 



73 

 755-1 

 755-3 

 755-2 

 757-1 

 757-2 



757-3 

 756-2 



756-i 



756-3 



Of all the specimens examined those from Riga, Vermont, are 

 available in the largest numbers and vary most in thickness. Their 

 forms are extremely simple varying from nearly spherical to thin, wa- 

 fer-like disks with but few irregular shapes. They are therefore favor- 

 able specimens for study. Of the twenty-two from this region 

 examined, the twelve with specific gravity below 2.70 have 

 a modulus below 5. The ten specimens with specific gravity 

 above 2.70 have a modulus above 5. Thus the modulus of 

 rotundity seems to increase in a general way with the density. 

 It is probable that the increase in density with increased 

 thinness is only apparent and is really due to those defects inher- 

 ent in the "methods of determination which have already been 

 stated. 



Clay stones, as impure concretions, are subject to many purely 

 fortuitous variations in composition. It is of importance to note 

 that almost any such variations from normal composition will give 

 a specimen of greater specific gravity than the typical claystone. 

 The glacial clays in which claystones commonly occur are rock flours 

 of varied composition. As a general rule they consist essentially of 

 floured quartz, kaolin and kaolinized feldspars and calcite. Such 



