mainly as fingerprints. But there are a few major excep- 
tions. Bending motions of hydrogen atoms attached to 
unsaturated carbon atoms lead to absorptions which are 
highly characteristic and which yield useful structural 
information. In the fossil resins, the most important of 
these is the sharp band near 11.8 » (885 em-!) which can 
be attributed to out-of-plane bending of the two hydro- 
gen atoms of a terminal methylene group. The presence 
of this band in the spectrum of a fossil resin is of particu- 
lar interest, because it is also a feature of a number of 
resin acids which have been isolated from recent resins 
(agathic acid, copalic acid, catavie acid, eperuic acid), 
The absence of this band in fossil resin spectra, however, 
must be interpreted with caution, since terminal methy!] 
groups are easily oxidized. The lack of an 11.3 p» (885 
em-!) band in the spectrum of a fossil resin may, there- 
fore, indicate either that the resin never had a terminal 
methylene group or that this group has been oxidized as a 
result of long exposure. The hydrogen atoms attached to 
aromatic rings also cause easily recognizable absorptions 
in the upper regions. ‘They are rare in fossil resins, but, 
when they occur, they permit immediate assignment of 
the resin to the few botanical sources characterized by 
aromatic components. 
All of the spectra were made from amber in the solid 
state which was dispersed in potassium bromide pellets 
(Langenheim and Beck, 1965; Beck et al., 1965). The 
Perkin Elmers Model 137 spectrophotometer was used 
for the samples reported in this section. 
The spectra curves reproduced here can, of course, be 
only a small fraction of those now recorded in both of 
our laboratories. ‘Io make the selection, we have com- 
pared all the spectra of each species or variety in order 
to choose a few spectra which best represent the group as 
a whole. In addition, we have included spectra of special 
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