254 REPORT OF NATIONAL MUSEUM, 1904. 



grouped all organic relics under nine heads, as follows: Genus I, 

 Mammodolite; Genus II, Ornitholite; Genus III, Amphibiolite; Genus 

 IV, Ichthyolite; Genus V, Entomolite; Genus VI, Helmintholite; 

 Genus VII, Concholite; Genus VIII, Erismatolite; Genus IX, 

 Phytolite. 



In 1821 Eaton was employed by S. Van Rensselaer to make a geo- 

 logical and agricultural survey of Rensselaer County, New York. His 

 report, printed in 1822, formed an octavo pamphlet of 70 pages, and 



was accompanied b} r a geological section, extending 

 Ren°sseiaef u county° f f rom the Onondaga Salt Springs across the county to 



Williams College in Massachusetts. The first thirty 

 pages of the report were given up to discussions of the character and 

 distribution of the various kinds of rocks and soils, and the remainder 

 to methods of culture and an agricultural calendar. 



The rocks of the county, as well as those of Washington County on 

 the north and of Columbia County on the south, were regarded as chiefly 

 belonging to the transition formations. Secondary limerock resting 

 on the graywacke was found in Schaghticoke about four miles east of 

 the Hudson and in the northern part of Greenbush. As to whether 

 the argillite along the eastern margin of the county was transition or 

 primary, he was in doubt. As with his contemporaries, he based his 

 opinions largely upon lithological data, quite failing to realize that 

 rocks of widely varying age may more or less resemble each other, 

 according to local conditions and the amount of metamorphism they 

 may have undergone. Passing westward from Williams College, the 

 various rocks met with, as shown in his section, and described are (1) 

 granular and primitive limestone, (2) metalliferous or transition lime- 

 stone, (3) argillite, (4) metalliferous limestone again, (5) a second band 

 of argillite, (6) graywacke with sporadic patches of (7) compact second- 

 ary limestone, (8) secondary or calcareous sandstone, and (9) argillaceous 

 gra} T wacke, semi-indurated argillite, and clay slate. The first three 

 were represented with steep westerly dips passing under the gray- 

 wacke, which constitutes the principal formation. 



On November 17, 1820, the Hon. J. B. Gibson read a paper before 

 the American Philosophical Societ} 7 , which was published in the 

 Transactions of that year, on the trap rocks of the Conewago Hills 



near Middletown, Dauphin County, and Stony Ridge 

 TrapRock S T82o n near Carlisle, Dauphin County, Pennsylvania. He 



described the mode of weathering into bowlders, and 

 rightly argued that such was due wholly to atmospheric agencies and 

 did not indicate an original concretionary structure. He seemed to 

 regard the columnar structure in this class of rocks as due. also to 

 decomposition, mentioning as an example the columns of the Giant's 

 Causeway, "which exhibit regular prismatic form only when it has 

 long been exposed to the action of the atmosphere." 



