F. B. Meek—Age of the Lignitic formation, etc. 459 
are usually accompanied by implanted crystals also of ripido- 
lite and magnetite, and sometimes by those of dolomite. The 
chondrodite, ripidolite and magnetite of the veins ‘are often 
overlaid by a crystallization of dolomite afterward introduced 
(perhaps immediately afterward), and in places by that of bru- 
cite. But crystals of ripidolite sometimes overlie chondrodite, 
and rarely are imbedded in a crystal of chondrodite;_ bril- 
liant crystals of chondrodite occur isolated in the dolomite and 
in the brucite; and grains and crystals of magnetite are often 
imbedded in the dolomite: showing that all these minerals 
were made, at one epoch, and together. The crystallization of 
most, but not all, of the chondrodite of a vein preceded the 
deposition of the accompanying dolomite. 
3. Pseudomorphism not “ Envelopment.” 
ae 
Arr, XLITI.— On the age of the Lignitie formation of the 
Rocky Mountain region; by Mr. F. B, Mrex. 
[On this important question in American geology, Mr. Meek has 
presented a learned discussion in Hayden’s Report for 1872, from 
dlemat: d 
near Bear River, Wyoming, a bed above the principal coal bed is 
full of good specimens ; at Coalville the shells occur both below 
and above the main coal bed, through arange of beds having in 
all a thickness of 4,680 feet; all but 400 feet of this series lie 
above the great coal bed. Moreover, none of the s ] 
Tnoceramus—which are mostly casts—bear any evidence of having 
been washed out and transferred from an older formation. 
Besides Jnoceramus at different levels, there is a species 28, 
