Beach Stnicfitrc in Medina Sandstone. — FaircJiild. 9 
BEACH STRUCTURE IN MEDINA SANDSTONE. 
H. L. Faikchild, Rochester, N. Y. 
PLATES II-VI. 
Since Dr. James Hall published, nearly sixty years ago, his 
"Geology of the Fourth District," the Ivledina sandstones of 
western Xew York have been regarded as shallow-water de- 
posits. On pages 34 to 57 of that remarkable work he describes 
the markings which occur in great profusion in the sandrock 
and compares them with the features that he had studied on 
the living beach of C)ntario. It is a fine example of inductive 
reasoning, and seemed to determine past all question the shoal - 
water genesis of the Medina sands. While the lower strata 
and the clavey beds were thought to indicate relatively deeper 
water, the quartzose bed, as at Lockport and "Medina, were 
^'evidences of a sandy beach which was alternately washed by 
the advancing and retiring waves and again left dry and above 
their reach." 
Subsequent workers on the Medina have followed Dr. 
Hall's conclusions, apparently without question, until a recent 
paper by Dr. Gilbert, which interprets certain curving and 
crested structures in the sandstone as "giant ripples" formed 
in deep ocean.''' 
In examination of the Medina sandrock in numerous ex- 
posures and quarries between Rochester and Lockport the 
writer has found no reason for questioning its origin as beach 
sands, and believes that the ridges and hollows in question are 
typical beach structures. In this paper it is proposed to briefly 
state the facts and argument. 
Character of the Sand Rock. 
The red Medina of western New York, 1075 feet thick at 
Rochester, is mostly an arenaceous shale and unfit for building 
material. In the upper horizon, and lying at the surface in 
the region of Brockport, Holly, Albion, Medina, and Lockport. 
are thick lenses of nearly pure sandstone, in great demand for 
paving and buildings. \"ery thin laminae of clay occur in the 
seams of the sandrock, ])articularly in the concave partings. 
Locally the clay may constitute definite beds or may alternate 
with the sand layers. The particular point is that the sand- 
• "Ripple Mark.s and Cross-bedding," Bull. Geol. Soc. Amer., 10-135. 
