224 Orishany Drift .— Cooper Curtice . 
they are supposed to have been transported by water or ice for 
some distance. As the nearest known rock like them is in 
the Shenandoah valley on the western side of the Blue Ridge 
some seventy miles to the westward, it is also supposed that 
they have been transported thence along the valley of the 
Potomac either by the currents or by floating ice. 
On a visit with friends to the Mecca of all loyal Americans, 
Mount Vernon, Virginia, during the spring of 1886, it was my 
good fortune to find within a rod or two of the tomb an 
angular fragment of rock which bore an unmistakable Oris- 
kany fauna. The guard was near and the rock is probably 
there yet as he seemed to think I wanted it for a souvenir; a 
search through the stone heaps in the ravines yielded other 
fossiliferous pieces, however, and partially appeased me for the 
loss of the coveted fragment. A few days later I went to a 
point about a mile below Alexandria and was rewarded by find¬ 
ing quite an addition to those species already found. Since 
then I occasionally find fragments of fossils in the cobbles 
used in paving many of the gutters and car tracks throughout 
this city. 
Mr. R. R. Gurley, of the National Museum, has lately iden¬ 
tified the fossils found and kindly furnished me with a list. 
They are as follows : 
Mount Vernon. Alexandria. 
TJnd’t coral. “ 
Ortkis hipparionyx Vanuxem,.“ 
Spirifera arenosa Conrad,.. “ . “ 
Cyrtina rostrata Hall,. “ 
Leptsena flabellites Conrad,.“ 
Rensslaeria marylandica Hall,.“.“ 
“ suessana Hall,. “ 
Megambonia lamellosa Hall..“.“ 
Avicula textilis var. arenaria Hall,. “ . 
Und’t lamellibranch (2sp). “ . “ 
Platyceras ? (1 sp).\. “.. 
Homalonotus.“.“ 
7 10 
The interest of this discovery lies in the determination of 
the horizon to which these loose drift stones of the Potomac 
formation once belonged. The only statement that I have 
seen regarding their supposed age is that by Rogers in the 
Geology of Virginia in which it is asserted that they are of 
Potsdam age. This determination must have been made from 
the resemblance of these stones to the strata of a formation in 
