Report of the Director. 11 



We have seen, from the remains of a Palgeozoic forest discovered last 

 year near Gilboa, that during the period of the Hamilton and 

 Chemung groups, the land was encroaching upon the sea ; not simply 

 by extending itself seaward in accumulations, but also by the process 

 of alternate elevation and subsidence. The remains of the forest of 

 Psaronius had been again submerged and covered by beds bearing 

 marine forms. 



During this period, while one portion of the coast became elevated 

 above the water-line, the adjacent ocean-bed or littoral area was also 

 extended ; because the submarine portion likewise participated in the 

 movement. As the elevation went on, the portion occupied by 

 littoral species became essentially dry land, and the area of littoral 

 species was pushed farther seaward ; the deposits from the nearer 

 shore, which were of coarser texture, covered the finer mud with its 

 living forms and supported a new fauna. 



In this manner a fauna, at one time inhabiting a belt in proximity 

 to the shore line, may, by the gradual deviation of the coast, slowly 

 extend seaward, accompanied all the time by the same kind of sedi- 

 ments and similar physical conditions ; thus encroaching upon the 

 area of and gradually covering the deeper sea forms of animal life. 



The reverse of this movement will take place when the coast line 

 subsides ; for the source of sediments becoming farther removed, the 

 water deepening, and the finer muds coming in, make the conditions 

 unfavorable for littoral species ; while those of the deeper sea-bed 

 invade the area temporarily occupied by the littoral forms, and 

 follow shoreward the slowly subsiding land. In this way occur the 

 alternating beds of coarser and finer sediments, charged with the 

 faunal remains which, when living, were adapted to the conditions 

 existing during the deposition. 



By the careful collection and study of the fossils which occupy 

 the successive beds of different sediments, we may be able to attain 

 at least some proximate knowledge of the successive periods of eleva- 

 tion and subsidence of the coast line, during a given geological 

 period. It seems to me, moreover, that by such critical study and 

 by noting the nature and thickness of each of these distinct beds, we 

 may be able to indicate the longer or shorter continuance of the 

 periods of elevation or subsidence, of which we trace the final result 

 in the permanent extension of the land. 



To accomplish such determination as shall be of any value, requires 

 a long series of observations and collections, to be both carefully 



