MEANING (3F CHANGE OF THICKNESS IN FORMATIONS 181 



the sections occup}^ in relation to each other express approximate!}^ their 

 relative distances from a shoreline to the eastward. The letter R is placed 

 at the point of first considerable deposition of red sediments for the 

 eastern sections. It will be observed that this is over 7,000 feet down in 

 section I, about 6.000 in H, 3,000 or 4,000 down in G, 1,200 in F, and 

 300 in E. Where these red sediments prevail the marine faunas cease, 

 and fossil fish and plants and some invertebrates which are supposed to 

 have lived in brackish water occur. In relation to the marine faunas 

 this horizon, at which pure marine conditions were cut off, occurs at an 

 increasingly later period for each successive section on passing westward. 

 This fact may be interpreted as evidence that the shoreline gradually 

 advanced westward with the passage of time, at least after the appear- 

 ance of the New Milford red shales in the Monroe county, Pennsylvania, 

 section (I) (see R of section I). 



The three Types of Sediments and their Associated Faunas 

 a. the red shales and sandstones 



The sediments may be classed in three types or facies, to use the classi- 

 fication of Renevier in his " Chronographie Geologique." 



Type A includes the red shales and sandstones, such as are seen in the 

 Montrose, Oneonta, Catskill, and Mauch Chunk formations. These, it 

 will be observed, are at the eastern end of the series. There they are 

 not in evidence at the bottom, but as we pass upward they first appear 

 in the easternmost sections; then farther west, and at the top of the 

 series have reached nearly to the westernmost of the sections. They 

 carry a fish fauna, Holoptychius, a few invertebrate fossils and plants, and 

 appear to have been rapidly accumulated and in an estuary, or at least 

 on not fully marine bottom. Far to the east, in Maine and New Bruns- 

 wick, similar sediments, with a similar fauna and flora, occupy all that 

 part of the column which is occupied in New York by formations between 

 the Oriskany and Carboniferous. In that region no marine faunas cor- 

 responding to the marine faunas of the Devonian of New York occur of 

 younger age than Oriskany. 



B. THE ARGILLACEOUS SHALES AND FINE GRAINED SANDSTONES 



Type B, the second type of sediments, is represented by the rocks of 

 the Hamilton, Ithaca, Chemung, and Waverly formations. They are 

 alternating argillaceous shales and fine grained sandstones, bearing a 

 rich and varied marine fauna. At the bottom they are best represented 

 in the easternmost sections, but they also transgress westward as we as 



