zone and in the lowermost part of the overlying sand- 
stones and shales. 
The geologic history inferred tor the Simojovel Group 
suggests deposition of sediments, derived from the an- 
cestral Sierra Madre to the south, under warm, generally 
shallow-marine conditions. Occasional shoreline oscilla- 
tions led to deposition in terrestrial, estuarine and brack- 
ish environments. 
DESCRIPTION OF SAMPLES FOR POLLEN ANALYSIS 
The samples analysed for pollen were collected by J. 
Wyatt Durham and Jean H. Langenheim from beds in 
which the amber occurred or from immediately adjacent 
beds (Plate NXNNVIII). In general, the amber from 
these deposits does not appear to be reworked: hence it 
may be possible to determine some of the vegetational 
conditions at or near the depositional site. Location of 
sites from which samples were studied are indicated in 
Plate NN XIX. Lithologic description of the 12 samples 
is presented in the Appendix. Most of the samples were 
either calcareous siltstones or silty shales, three of the 
latter being glauconitic. There was some variation in 
coarseness and in color. One sample was a calcareous 
sandstone. Several samples were associated with lignitic 
bands or at least had carbonaceous streaks. 
All of the samples are from the upper portion of the 
Simojovel Group and of latest Oligocene or earliest Mio- 
cene age (Durham 77 /it., 1964). Samples from Simojo- 
vel, Mazantic, Pabuchil, Huitiupan, Portugal and Las 
Cruces (I-VII) are believed to be of approximately the 
same age (Durham, pers. comm. 1965). Durham also 
indicated that stratigraphic control on Sample NIT from 
Jolpabuchil has not been established. R. C. Allison (77 
fit. to Durham) considers the invertebrate fauna from 
Mina Palo Blanco and Mina de Naranjo to indicate an 
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