the Upper Devonian of Iowa. 363 



ster and F. concentrica multisinuata Fenton, and may- 

 be referred to as the Gigantea faunule. The second is 

 distinguished by the large numbers of finely preserved 

 brachiopods, and in it the genera Atrypa, Schizophoria, 

 Strophonella, Douvillina and Spirifer reach the height 

 of their development in the Hackberry. Corals are 

 plentiful ; stromatoporoids are by no means lacking, and 

 at Rockf ord there are very large numbers of bryozoans 

 in this horizon, yet it is primarily a horizon of brachi- 

 opods, and may be referred to as the Hystrii faunule. 

 The third division is not so rich in gastropods nor brachi- 

 opods, but is characterized by great numbers of 

 stromatoporoids and corals. Chonophyllum, Characto- 

 phyllum, Zaphrentis, Pachyphyllum, Macgeea, Alveo- 

 lites, Stromatoporella, and Syringostroma are at their 

 height, with the last two genera in particular abundance. 

 This division may be referred to as the Stromatoporella 

 faunule. 



At the pits of the Rockford Brick and Tile Company 

 the two lower faunules are developed. The species Nati- 

 copsis gigantea occurs in the "wrinkled' ' form of the 

 original description, and Floydia concentrica occurs in 

 considerable numbers. The Hystrix faunule is very well 

 developed, with that species and the genus Spirifer as 

 the predominating forms along with A. reticularis. At 

 these pits the Stromatoporella faunule is lacking, but to 

 the north and west we again find it in place and charac- 

 teristically developed. Three miles southwest of Rock- 

 ford, at what is locally known as Bird Hill, an exposure 

 by the roadside has several features of interest. Here 

 the lower exposed beds are of quite hard shale, evenly 

 stratified, and everywhere crowded with fucoids. There 

 is an interesting parallel with the beds of the Striatula 

 zone at Mason City, for the fucoids of the lower portion 

 of this member are smaller, less inclined to branch, and 

 much more numerous than those of the upper portion 

 of the bed. These latter branch frequently, have a thick- 

 ness of two to as much as five inches and an apparent 

 length, at times, of three to four feet. Above these 

 fucoid beds are the shaly clays containing the Hystrix 

 faunule, which is here very rich in both brachiopods and 

 bryozoa. 



A quarter of a mile to the west of Bird Hill, and still 

 on the same ridge, is a cut that shows beds containing 



