English: Plate XXIII from The Geology of the Richmond Basin published by USGS, which has the following caption:
Argillaceous arkose containing fragments of porphyritic feldspar in basal beds, Etna Shaft, Mildlothian.
The text of the report states this:

A peculiar variety of feldspathic rocks found on the eastern margin of the basin consists of a matrix of carbonaceous compact clay interspersed with quadrangular cleavage pieces of the large porphyritic feldspars of the granitite (see Pl. XXIII). The means by which these feldspar fragments were dispersed in the clays without accompanying grains of quartz and the more minute feldspar fragments is not in accordance with the ordinary work of running water. Wind or floating ice is apparently demanded for the transportation of the feldspar grains, since currents of water strong enough to bring the large feldspar pieces to the area of deposition would have swept away the mud; moreover, such currents would have assorted and stratified the materials.

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