EFFECT OF CONDITIONS OF SEDIMENTATION. 45 



may well lead geologists all over the world to consider the question : How 

 large a part of the stratigraphic succession of life, which is made so much of 

 by the careful noting of zones, is only local-condition succession ? Walcott's 

 discovery, in the Eureka Devonian beds, that many species of the New 

 York, Hamilton, and a few Chemung species occur in the Lower Devonian 

 of Eureka and some Lower Devonian of New York in the Upper of Eureka* 

 give emphasis to the reasons for careful and comprehensive study before con- 

 clusions as to biological succession are endorsed " established." 



I might illustrate also the influence of the varying conditions, in such a 

 Northeast Bay, on rock-making, but add only a single thought. In the 

 matter of the tides, how exceedingly varied are the circumstances that 

 would have attended deposition in consequence of the changing positions and 

 force of the tidal currents which variations in depth and other causes would 

 have occasioned ! Conglomerates would have been formed where the cur- 

 rents were strongest. But, in the same long geological epoch, the strongest 

 tidal current out of the great Northeast Bay might have had many different 

 positions over western New York or Pennsylvania or over eastern Ohio, 

 and thus conglomerates would have been made at various levels, which the 

 geologist might, unless cautious, take as equivalents. 



The Central Interior and Western Interior regions I pass without special 

 remark, although they derive great interest from study parallel with that of 

 the Eastern Interior. 



The Pacific Border region owes its maximum width, which occurs in the 

 United States portion, to the east and west bend of the Archaean protaxis of 

 the Rocky Mountains in Wyoming and Southern Montana. This Archaean 

 bend carries eastward, in a somewhat irregular way and more than 250 miles, 

 the part of the protaxis south of the bend. 



Over the Pacific border, there are, as has been recognized, two prominent 

 lines or series of mountain ranges nearly parallel with the coast: (1) The 

 Coast chain, which includes the Coast ranges south of Vancouver's Island, 

 and the island ranges along the coast northward ; (2) The Cascade chain, 

 as it may be called, including the Sierra Nevada, the Cascade range of Ore- 

 gon and Washington Territory, and ranges of mountains in British America 

 that are nearly in the same line. Neither chain has a well-defined Archaean 

 axis except for a small part of its course, and this is probably owing to the 



*C. D. Walcott, Paleontology of the Eureka District, 298 pp., 4to., with 24 plates of fossils, 1884, U. 

 S. Geological Survey. The lower part of the Eureka Devonian limestone contains many Upper 

 Heiderberg species'of New York and other States east o( the Rocky Mountains. But with these are 

 manv that are Middle and Upper Devonian in New York and elsewhere; among these, the three 

 Hamilton Tentaeulites, T. attenuates, T. bellulus, and T. graeilistriatus. Besides this, some New 

 York Upper Heiderberg species are found in the upper part of the 6000 feet of Devonian limestone, 

 as Cladopora proliftca Hall, Chonetes mucronata Hall, Euomphalus laxus Hall ( Upper Heiderberg and 

 Hamilton in New' York). Again, many of the species of the lower part occur also in the upper, 

 showing long survival of individual forms— e. g.,Streptorhynchus chemungensis, 4 species of Productus, 

 Chonetes defiecta, Strophodonta perplana, 2 species of Spirifera, a Paracyclas, Styliokt ftssurella, 

 Rhynchonella castanea Meek (a Mackenzie river species). 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. 



