LATER MESOZOIC INVERTEBRATE FAUNAS 189 



totally different facies, bespeaking very dissimilar conditions. If 

 there had been direct and free marine connection between the two 

 areas it is probable that the conditions could not have been so different 

 and the faunas would have shown less contrast. That the two faunas 

 were approximately contemporaneous and that there was no impor- 

 tant break in the sedimentation of either area during this epoch are 

 well determined facts. It is believed, therefore, that there was a 

 long land mass approximately parallel to the present west coast sep- 

 arating the two provinces. 



In considering the Comanche area, as mapped, it should be remem- 

 bered that a long period during which thousands of feet of limestone 

 were formed is represented, and that the sea was advancing toward 

 the north. The best-known early Comanche fauna is found near 

 Tehuacan in the state of Puebla. It has been suggested with some 

 reason that this is possibly in part somewhat older than the Trinity 

 group which forms the base of the Comanche in Texas. It is largely 

 a reef fauna consisting of corals and other sessile animals with other 

 forms that are usually associated with them. Farther north one 

 facies of the Trinity group fauna is characterized by an abundance 

 of Orbitolina, while another facies has more of a littoral character. 

 Trinity strata and fossils are found as far west as Bisbee, Arizona, and 

 north to southwestern Arkansas and southern Oklahoma. 



The succeeding fauna of the Fredericksburg group also has both 

 littoral and reef facies. The latter is characterized by an abundance 

 and great variety of Rudistae, Chamidae, and Caprinidae with Ne- 

 rinea, etc., usually occurring in very pure limestone, but this facies is 

 in some areas repeated in the Washita group so that the two faunas 

 are sometimes hard to distinguish. The reef facies does not reach 

 the northern boundary of Texas and the Fredericksburg fauna as a 

 whole is not definitely recognized beyond that line though it is possibly 

 represented at the base of the Kiowa shale of southern Kansas. 



The reef facies of the Washita fauna is not found north of southern 

 Texas but the littoral facies extends far beyond the limits of the 

 Trinity and the Fredericksburg into northeastern New Mexico, 

 southern Colorado, and middle Kansas. The thin Comanche depos- 

 its in all these areas belong exclusively to the Washita group and 

 probably to the upper Washita. They rest at some localities on the 



