English: Plate XIX from The Geology of the Richmond Basin published by USGS, which has the following caption:
Porphyritic granite from bottom of Etna Shaft, Midlothian.
The report refers to the figure as follows:

The term geologic basin implies a mass of strata surrounded on the present surface aud underlain by rocks of more ancient date, presenting frequently a marked difference of attitude and invariably of structure; at least such is the conception gained if we examine the areas to which the name basin has been, in the common use of geologists, applied. Of the distribution of the rocks of this earlier group beneath the Richmond Basin we have as yet no knowledge other than those apparently valid suppositions which may be based upon a fair interpretation of the dominant structure of the rocks about its margin.

The porphyritic granitite.—The bordering rock on the eastern side of the area is a coarse porphyritic granitite, well developed in the vicinity of Midlothian, and extending with variations of texture as far north as Gayton and as far south as Winterpock. Its large porphyritic crystals, often in the form of Carlsbad twins, are arranged in a general north and south direction, due to the flow of the once fluid rock (see Pl. XIX). The disintegration of these feldspars has played an important part in the development of the Newark sediments.

The Etna Shaft was located approximately at 37.512 N, 77.638 W, on the west side of the Southern Railway.