Maryland Geological Survey 123 



simple. The amount of each portion is represented by a vertical column of 

 which the height corresponds to the percentage of the portion present in 

 the whole sample. The columns are all of the same arbitrary width and the 

 successive sizes are placed side by side, the vertical boundaries between 

 them being the limit of size that separates them. Their significance may 

 be most readily conceived by imagining the columns to represent small 

 sample tubes containing the different portions and placed side by side in 

 order of their size of grain. 



Finally, mention must be made of a serious defect in the entire analysis 

 of many samples, which arises from the abundance of carbonaceous organic 

 matter present. Even a determination of it by quantitative analysis, if it 

 did not involve an amount of time disproportionate to the advantage to 

 be derived, would probably not give entirely accurate results. Keilhack * 

 describes a common method of determination by burning off the carbon- 

 aceous matter, but this has so many defects that it scarcely seems worth 

 using. It is probably largely on this account that the Bureau of Soils of 

 the Department of Agriculture takes no cognizance of carbonaceous 

 matter, which practice has been followed in the present study. However, 

 a specific gravity separation might be used here to float off the carbon- 

 aceous matter, at least in the sands, w T ith results of a degree of accuracy 

 equal to that of the other separations. Certainly in some of the sediments 

 that in the following pages have been called of the " delta " type the pro- 

 portion of carbonaceous matter is so great that it interferes seriously with 

 the value of the results of the analyses. 



'Keilhack, Lehrbuch der praktischen Geologie, 1908, p. 540. 



