June, 1906. New Forms or ConcreTIONS—NICHOLS. 53 
35 2.68 3.4 ._ Connecticut River 805-1 
Ree 2-055 516°3.3 iy 55—I 
e's | 3.2 2 76-3 
Zone. 05.2.0 ens 805-3 
SO get Ooh) 2.7 - 7 5—2 
AOnE a Oi = 3 §.3 76-1 
41 2.67 3.4 : 70-3 
Wok 2 071-11 3.4 i 805-9 
43 2.70 12.0 Hartford, Connecticut. a 
‘44 2.76 3.0 Deerfield, Massachusetts. 753-2 
45 82273) 61.6 Zi : 753-1 
46 2.93 16.4 South Hadley, Massachusetts. 73 
47 2.71 8.1 Charleston, New Hampshire. Woe] 
AG 2207 "9.2 , i 755-3 
49 2.66 3.9 a < 7 755~2 
50 2.78 . 7.8 Cumberland, Maine. 757-1 
Rare PFs 2 4 hs "f 757-2 
Beas 0." '< 2.3 ir f 757-3 
53 2.68 5.4 Broad Cove, Maine. 7560-2 
pee ae Oia fs 3-4 - % 756-1 
Soe 2-037") 1.4 ss . 750-3 
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. 
Claystones, 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 
