interest since they show features not shared by all mem- 
bers of the group. 
We should like to warn researchers not to put too 
much weight on a single infrared spectrum of any fossil 
resin. Resins are mixtures of appreciable heterogeneity, 
and the small samples used to prepare spectra may well 
differ significantly in composition, even when taken from 
a single specimen. It is always advisable to run two or 
more spectra of a given specimen and to rely only on 
those features which are common to all or, at least, to 
most spectra. 
Relatively few of the North and South American am- 
bers have been characterized chemically or physically and 
assigned mineralogical species names, as numerous of the 
European ambers have been. In some instances, how- 
ever, paleobotanical remains of considerable significance 
in determining the botanical source of the amber have 
been reported in New World deposits. For this reason, 
botanical information regarding the kinds of trees that 
might have produced the amber, in addition to the man- 
ner in which the resin may have been produced, have 
received particular attention in this presentation. Con- 
fusion regarding stratigraphic data and, hence age as- 
signments of the amber-bearing strata, are discussed 
where relevant to an understanding of the rapid evolu- 
tionary changes which occurred in some of the possible 
resin-producing components of Cretaceous floras in par- 
ticular. Spectra of modern resins will be compared with 
those of ambers in some cases. Only general comments 
regarding the origin of the amber will be made, however, 
since this paper is designed primarily as a catalogue. 
Detailed discussion of botanical origin will be presented 
elsewhere. 
