PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 159 
gray to about the same extent asin the type. The superciliary stripe 
is very conspicuous and quite continuous. Bill and feet as in the pre- 
ceding. Wing 5.20, tail 4.15, culmen .80, tarsus 1.25, middle toe .90. 
It thus appears that the characters of the species, as originally de- 
fined by Professor Baird (Review Am. Birds, p. 29), are not only quite 
constant but also very pronounced, so that there need be no further 
reason for denying it the specific rank to which it is clearly entitled. 
MARCH 9, 1883. 
PRELIMINARY NOTE ON THE CRYSTALLINE SCHISTS OF THE DIS- 
TRICT OF COLUMBIA. 
By GEORGE P. MERRILL. 
As is well known, the region about Washington, D. C., is very poor 
in crystalline rocks, they being confined entirely to that narrow portion 
of the District in the immediate vicinity of Rock Creek and the strip of 
country to the westward included between the creek and the Potomac 
River. 
It is probably due largely to this poverty of material that these 
rocks have been so little studied, the only reference to the character of 
the formations that I am able to find dating back nearly fifty years. It 
is as follows: 
‘Rock Creek and its immediate vicinity is the line between the prim- 
itive formation and the Tertiary. From Rock Creek up the Potomac 
the borders of the stream are pregnant with primitive rocks in situ and 
in bowlders, with the exception of afew small pieces of alluvial soil here 
and there in the valley of the river. This is the case for 20 miles 
or more, when the country changes to old red sandstone, which con- 
tinues 20 or 25 miles farther up the river, with occasional ridges of 
breccia, or pudding-stone. * * * About amile, however, east of the 
entrance of Rock Creek into the Potomac, on the southern point of the 
city, near the glass-house, the final termination of the primitive rocks 
that line the bed and banks of the Potomac above clearly takes place. 
In digging wells beyond this point rocks seldom obtrude; the alluvial 
soil everywhere prevails. Rock Creek separates the primitive from the 
alluvial soil. In the former gneiss abounds, which is succeeded by 
amphibolic rock, or griinstein. The gneiss contains small crystallized 
tubes of magnetic iron, veins of feldspar, and quartz of opaque white 
color. * * * The rock employed to form the foundation, or base, of 
the houses in Washington is a species of gneiss composed of feldspar, 
quartz, and mica, of a leafy texture owing to the abundance and dis- 
position of the mica. It contains primitive sulphurous iron, and also 
particles of the same metal which are attracted by the needle.”* 
*From ‘‘A new and comprehensive Gazetteer of Virginia and the District of Colum- 
bia.” By Josiah Martin. Charlottesville, 1835. 
