The beginnings of the Permian flora in Pennsylvania 
extend far down into the Carboniferous. Certain Per- 
mian precursors are almost coextensive with the Steph- 
anian. The earliest appearances of Stephanian pecopterids 
occur in Middle Allegheny following the deposition of 
the Vanport marine limestone. Numerous lower Alle- 
gheny and even Pottsville plants persist, but here is the 
key to the whole problem. The next marine incursion 
eliminates the Pottsville-Allegheny complex and results 
in a new flow of migrants from the north-east (presum- 
ably Europe). 
There are five distinct marine invasions in the Upper 
Pennsylvanian rocks of western Pennsylvania. Each ma- 
rine invasion resulted in a local extermination of the ter- 
restrial fauna and flora. Repopulation of the region sub- 
sequently was effected by migrants from districts nearby, 
where the topography had not been so seriously altered. 
During the interval between the Vanport limestone 
(Middle Allegheny) and the Brush Creek limestone 
(Lower Conemaugh), the flora is essentially the New- 
ropteris ovata facies in association with Stephanian pe- 
copterids and mariopterids of the Mariopteris nervosa 
group. 
Three marine limestones occur in the middle third 
of the Conemaugh Series: Pine Creek, Woods Run, and 
Ames. The most extensive of these is the Ames lime- 
stone—a persistent bed with the following faunule: /'n- 
teletes hemiplicatus var., Spirifer cameratus, Ambocoelia 
planoconvexa, Chonetes granultfer, Productus  cora, 
Lophophyllum profundum, and a fusiline. Professor C. 
O. Dunbar has identified the fusiline as T'riticites collu- 
mensis Dyunbar and Condra. Among the rarer forms in 
this faunule, are species of Pseudomonotis and Hdmondia. 
With the invasion by the Ames Sea, there is a 
marked floral change—a change which permanently al- 
[17 ] 
