ingly, he presented a system based upon: 1) resins de- 
rived from coniferous sources, 2) resins derived from 
angiosperm sources, 8) resins of uncertain geologic age 
and unknown botanical derivation or otherwise inade- 
quately characterized. Unfortunately, as previously 
noted, the botanical derivation often is not known or 
well substantiated; hence Paclt’s criteria of classification 
are difficult to apply. His recognition of these characters 
as primary criteria, however, may have a useful influence 
upon future investigations. 
The term ‘‘amber’’ has been variously used. In its 
strict sense, it has been synonymous with the succinites; 
various other names have been used for the retinites. On 
the other hand, in a wide sense, ‘‘amber’’ is used for all 
fossil resins. It is in this broad sense that I shall employ 
the term in this paper. 
Part of the difficulty in establishing a classification of 
fossil resins or ambers has been the chaotic state of mod- 
ern resin nomenclature. This has resulted probably from 
the complex nature of the material. In the study of 
ambers, the distinction between gums and resins is sig- 
nificant. The former are water-soluble carbohydrates ; 
the latter consist of substances soluble in hydrocarbons. 
If the material is entirely water-soluble, it is not likely 
to become fossilized. Some gums are only partially 
water-soluble, and hence are known as gum-resins. The 
principal constituents of resins are resin acids, with aro- 
matic and aliphatic acids also present in some cases. Free 
or combined with these acids are two somewhat different 
kinds of alcoholic compounds called resinols and resino- 
tannols or, collectively, resin alcohols. The third primary 
constituent is a resene, which is usually less abundant 
than the resin alcohols and quite inert. The resene ap- 
pears to act as a protective colloid, and its effect on the 
behavior of the resin toward solvents seems great (Barry, 
f 228 | 
