December 28, 1900.] 



SCIENCE. 



991 



teenth Street, deposits have been observed 

 which fail to fit into this series. This 

 cutting reveals, unconformably beneath 

 the Earlier Columbia and uncomformably 

 above the Potomac, a heavy deposit of loam 

 and gravel of a structure, composition, 

 texture and material simulating the Earlier 

 Columbia formation in its normal aspect, 

 save that the materials are more extensively 

 disintegrated and decomposed. The re- 

 semblauce of the deposit to the Earlier 

 Columbia is such that it might readily be 

 classed with that formation if found iso- 

 lated ; but in the Sixteenth Street exposure 

 the two deposits are juxtaposed and sepa- 

 rated by a well-defined unconformity — i. e., 

 the stratigraphy shows that the deposit in 

 question is materially older than the earlier 

 Columbia. On comparing the deposit with 

 the Lafayette, as displayed in the nearest 

 exposures of that formation on the west, 

 north and east, it is found to be so different 

 in materials and structure as to demand sep- 

 aration on lithologic grounds ; moreover, the 

 deposit is confined to a depression, or amphi- 

 theater, which did not exist at the time of 

 Lafayette deposition, but was produced dur- 

 ing the period of rapid degradation accom- 

 panying the post- Lafayette uplift ; so that it 

 must be discriminated from the Lafaj'ette on 

 the basis of homogeny as well as on that of 

 lithology. The interpretation of the deposit 

 is simple : it is evidently a record of an oscil- 

 lation during the post-Lafayette and pre- 

 Columbia time, which was not of such 

 amplitude and length as to inscribe itself 

 deeply in the local series of formations and 

 land forms. On seeking to correlate the 

 deposit with other elements in the coastal- 

 plain series, difficulty is encountered ; no 

 corresponding deposits are known either 

 southward or eastward in Virginia and 

 Maryland ; the nearest known deposits of 

 corresponding character and position are a 

 part of those found in southern New Jersey 

 and first grouped by Salisbury under the 



designation Pensauken, but afterwards di- 

 vided. 



In Dr. John M. Clarke's paper on the 

 ' Lenticular Deposits of the Oriskany For- 

 mation in New York,' this formation was 

 described as attaining in eastern New York 

 its greatest thickness south of Albany 

 county, where it is highly calcareous and 

 carries its normal fauna. In its extension 

 through central and western Nev? York its 

 deposits are wholly arenaceous and siliceous 

 and they alternately thin and thicken, thus 

 forming a series of lenticular beds which 

 are connected by thin sheets or wholly sev- 

 ered by the actual disappearance of the 

 formation from the rock series. Beginning 

 in Albany county, the formation has a thick- 

 ness of but one or two feet, thence westward 

 of Schoharie county it slightly thickens, and 

 again thins and actually disappears in south- 

 ern Herkimer county. Still farther west- 

 ward at Oriskany Falls, the typical section,, 

 it attains a thickness of some 20 feet. At 

 Manlius, Onondaga county, it has decreased 

 to about one foot, and at Jamesville, five 

 miles west, increases to three feet six in- 

 ches. Four miles west of here, at Brighton, 

 its thickness is one foot six inches, whence 

 westward, at Elm wood, one mile and a half 

 away, it thins to six inches. Again the for- 

 mation disappears from the rock series, the 

 eastern thinning edge of the next lens ap- 

 pearing first at Split Eock, near Syracuse, 

 thickening towards Marcellus Falls, five 

 miles away, and at Skaneateles Falls, six 

 miles further west, attaining a cross-sec- 

 tion of 18 feet; thence suddenly dropping 

 to ten inches at Auburn, six miles still 

 further west. This lenticular mass, desig- 

 nated the Skaneateles lens, appears to be the 

 largest of these lenticular deposits west of 

 Albany. From this point westward but 

 two inconsiderable lenses are observable, 

 the deposits being a thin sheet seldom over 

 more than a few inches across. 



This evidence is regarded as indicative 



