to make this large body of evidence accessible to inter- 
ested research workers in the form of a catalogue which 
will be divided into three sections: 1, North and South 
American; If, Europe; III, Asia and Africa. A fourth 
section probably will present spectra of resins from living 
plants. 
We have attempted to procure as many specimens as 
possible of each kind of fossil resin from the leading col- 
lections of the New and Old World. Samples used in 
this section were obtained from the Harvard University 
Botanical Museum Paleobotanical Collections; Harvard 
University Mineralogical Collections; Harvard Univer- 
sity Entomological Collections; Museum of Paleontolo- 
gy, University of California at Berkeley, United States 
National Museum (Smithsonian), New York Museum 
of Natural History and Museum fiir Naturkunde, Kast 
Berlin. 
Since infrared spectroscopy is not yet a method widely 
used by botanists and mineralogists, we will here include 
a brief discussion of the major absorption bands of the 
fossil resins and their significance. Infrared radiation is 
absorbed by matter to provide the necessary energy for 
the motion of atoms within a molecule. These motions 
may be relatively simple (stretching and bending of in- 
dividual bonds between two atoms) or they may be very 
complex (involving larger portions of the carbon skeleton 
of the molecule). The simpler motions predominantly 
lead to absorption at low wave lengths (2.5-8 uw; 4000 
to 1250 em:!). Because they are essentially independent 
of the rest of the molecule, their absorption bands are 
remarkably stable in position and are readily assigned to 
specific functional groups. Thus, the first absorption band 
of fossil resins at 2.9 » (8500 cm-!) is due to the stretch- 
ing of hydrogen-oxygen bonds; the bending motion of 
these bonds causes absorption at about 6.1 » (1650 em! ). 
[ 68 | 
