1888. ] 51 [Uhler. 
Baltimore these strata dip below the surface of tide, pass under the Albi- 
rupean at an angle of about twenty degrees and entirely disappear from 
view. 
Miles. 
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sienna 
sevrrome cd, shynta oe NUNN CP CLLCCORS. 
Reviewing the three alluvial formations which are passed over between 
the city of Baltimore and Chesapeake bay, we find that each is overlaid 
by a system of drift, that of the Baltimorean carrying angular erratics, 
mixed with compact quartz pebbles, all derived from the Archian rocks 
of the neighborhood, with the exception only of boulders of Potsdam 
sandstone probably dropped by floating ice. In the upper part of this 
mixed gravel, and commonly above it, rests the stratum of ferruginous 
conglomerate so conspicuous wherever this member of the series occurs. 
It is possible that this is the position in the series to which should be 
referred the thick beds of gravel and quartz drift that now chiefly lie 
exposed at or next the tops of some of the low hills north of Baltimore. 
Near the summit of the Albirupean, we observe loose strata of gravel 
and quartz-drift, capped by a crust of ferruginous sandrock composed of 
unusually coarse grains of quartz. This belt of rock is exceedingly thick 
in some places, as on the Severn river below Indian landing, where it 
