592 HISTORICAL GEOLOGY. 



The Devonian of California, mentioned on page 580, contains, according to Schuchert, 

 Favosites Canadensis, Cyathophyllum rohustum, Cladopora labiosa, Syringopora Maclwrii, 

 and is referred by him with a query to the Corniferous ; at Gazelle, in Siskiyou County, 

 occur Diphyphyllum fasciculum and Acervularia pentagona ; and he suggests that the 

 beds may be of later date (1894). 



In the lower part of the Eureka Devonian limestone (p. 589) occur, according to 

 C. D. Walcott, the follov?ing Corniferous or Lower Devonian species of New York, etc.: 

 Favosites hemisphericus Y. & S., Cyathophyllum rugosum Edw. & H., Orthis impressa, 

 Stropheodonta perplana, S. punctulifera, Chonetes hemisphericus, C. mucronatus, Spirifer 

 raricosta, S. varicosus, Ati'ypa reticularis, Nucleospira concinna, Meristella nasuta, 

 Platyceras carinatum, P. conicum, P. dentalium, P. nodosum, Phacops rana, and many 

 others. But with these are very many that are Middle and Upper Devonian in New 

 York and elsewhere, and among these are the three Hamilton Tentaculites, T. atten- 

 uatus, T. bellulus, T. gracilistriatus. Besides, some New York Upper Helderberg species 

 are found in the upper part of the 6000 feet of Devonian limestone. Again, many of the 

 species of the lower part occur also in the upper part, showing long survival of individual 

 forms ; this is true of Orthothetes Chemungensis, of 4 species of Productus, Chonetes 

 deflectus, Stropheodonta perplana, 2 of Spirifer, Bhynchonella castanea of Meek (a Mac- 

 kenzie River species), a Paracyclas, Styliolina fissurella. Orthis McFarlani Meek is a 

 second Mackenzie River species ; and as the two are Lower Devonian in Nevada, they 

 may be so at the arctic localities. Many of the species are represented in the Devonian 

 of Iowa, or the Continental Interior, where the waters were purer and probably deeper 

 than in the New York Bay, and therefore more like those of the Eureka district. 



Of the Eureka Devonian species that are found only in the upper division, the follow- 

 ing are confined to the Lower Devonian in New York : Syringopora Hisingeri, Cyatho- 

 phyllum corniculum, and Chonetes mucronatus ; and the following are among those that 

 are Middle or Upper Devonian in New York or Iowa: Orhiculoidea minuta (Hamilton), 

 Orthis Tulliensis (Ham.), Productus lacrymosus (Chemung), P. speciosus (Ch.), Spirifer 

 disjunctus (Ch.), Athyris angelica (Ch.), Bhynchonella duplicata (Ch.), B. Laiira (Ham.), 

 B. sinuata (Ch.), Bellerophon mcera (Ch.). The preceding conclusions appear to be well 

 sustained, unless it may be that there are unseen faults in the limestone. See, further, 

 Walcott, Pal. Eureka, TJ. S. G. S., 4to, vol. viii., 1884, where 144 Devonian species are 

 described; and also Arnold Hague, Bep., vol. xx., U. S. G. S. 



3. Hamilton Period, or Middle Devonian. 



rocks — kinds, subdivisions, and distribution. 



The Hamilton group was so named from Hamilton, in Madison County, 

 N.Y. The beds have a wide range, like the Corniferous limestone. They 

 extend from eastern ISTew York (Schoharie County) westward to Iowa; but in 

 New York and Pennsylvania they are mainly shales and sandstones, of shallow 

 water origin, and wholly calcareous only in the Central Interior region. 

 Moreover, they have great thickness to the eastward, 1500 feet, but thin 

 down rapidly to the westward, being only 300 to 1100 feet thick near Lake 

 Erie, thinning down to 20 to 50 feet. They border Lake Erie in Ontario ; pass 

 by the south end of Lake Huron into Michigan, where they are limestone, 

 and 10 to 120 feet thick. They appear also in Ohio, as 25 feet of impure 

 bluish limestone; in Indiana, where at the Falls of the Ohio, above Louisville, 

 they are 20 feet thick, and include the hydraulic and overlying beds of the 

 limestone formation of the place. They occur also in Kentucky ; Illinois, 



