REPORT OF THE DIRECTOR. 9 



kill group, and one hundred and fifty feet above the beds of gray 

 and olive shales and sandstones, heretofore regarded as limit- 

 ing the Chemung group proper. From the position in which 

 the stratum occurs this slab is very interesting, carrying, as it 

 does, an assemblage of Chemung fossils rarely met with, in 

 like association, in typical localities of the group. Numerous 

 other specimens have been collected from the same stratum, 

 and will go into their proper places in the Museum. Such 

 collections have an interest beyond their character simply as 

 fossils, and they merit especial care in their preservation.* 



It is a serious misfortune that our Museum has not space to 

 admit of the arrangement of collections illustrating sections of 

 formations ; that is, collections of specimens of the rocks and 

 fossils from numerous points, both in the midst of formations, 

 and also at their junction, which shall illustrate the physical 

 and biological changes and conditions at successive stages of 

 the deposition. No geological or palseontological collection 

 will ever be complete, or afford full measure of instruction, till 

 such collections shall be made and carefully preserved. 



A large number of specimens, 2,413, some of them slabs 

 covered with smaller fossils, of the Lower Helderberg group 

 and Oriskany sandstone, f have been arranged in the drawers 

 beneath the cases representing these formations. This disposi- 

 tion is necessary because we have no cases for their exhibition. 



The geological collections from the Niagara group to the 

 Lower Pentamerus inclusive, have been re-arranged in the 

 new alcove cases. The collections of the lower rocks to the 

 Hudson river group and Medina sandstone, have been cleaned 

 and re-arranged upon the shelves. 



Many large and important specimens remain ready for 

 arrangement with the geological and palseontological collec- 



* These specimens present a beautiful illustration of the recurrence of previous 

 conditions of deposition after a long interval, — conditions existing through many 

 hundreds of feet of sedimeutary accumulations with organic forms, but which 

 had ceased, and, other influences supervening, had accumulated a great mass of 

 non-fossiliferous red shales and sandstones, belonging really to a different geologi- 

 cal era. These facts, moreover, illustrate the impossibility of drawing any strict 

 lines of demarkation between different groups as represented by sedimentary strata. 

 The simple explanation is, that, owing to oscillation of the sea-bed, the shore-line 

 was advanced, and the encroachment of littoral deposits either destroyed or pushed 

 far seaward the then existing organisms, which again, after an interval, returned 

 to the same areas, by the recession of the shore-line or sinking of the ocean-bed. 



+ Of the Lower Helderberg, 1,976 specimens, and, of the Oriskany sandstone, 437 

 specimens. 



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