430 New York Stale Museum 



The fauna of the Knapp bed includes, in addition to 

 the Devonian survivor Spirifer disjunctus, several species 

 of Leptodesma, Rhynchospira scansa and Athyris polita, 

 probably restricted to this horizon, and such representa- 

 tives of basal Mississippian (Kinderhook) genera as 

 Productus, Syringothyris and Shiimardella. The Missis- 

 sippian age of the Knapp can not be doubted. Above this 

 fauna remains of the tree fern Archaeopteris obtusa oc- 

 cur well up toward the bottom of the Pottsville (Butts). 



Literature. For the general discussion of the period 

 are recommended the textbooks suggested for the preced- 

 ing periods, also Schuchert ('10) and Ulrich ('11). 

 Among other papers that may be consulted are Butts 

 ('03), Carll ('90), Chadwick ('24), Clarke ('03), Glenn 

 ('03), Hartnagel ('12), Lobeck ('27) and Williams 

 (•87). 



MESOZOIC ERA 



The Mesozoic era includes formations that were among 

 the first of the stratified rocks known to geologists. The 

 name, meaning "middle life," was given to this group of 

 formations in comparatively recent times. Mesozoic 

 rocks were first studied in greatest detail in England. 

 The era covers about one-tenth (11 per cent) of geologic 

 time and includes the Jurassic, Triassic and Cretaceous 

 periods, the last named comprising the Lower Cretaceous 

 or Comanchean and the Upper Cretaceous or Cretaceous 

 proper. 



Triassic Period 



The name Trias was applied to a group of three forma- 

 tions in northern Germany in contrast to a twofold series 

 (the Permian) below. From this the name Triassic 

 gradually came into use. As a result of the Appalachian 



