148 Association of American Geologists and Naturalists. 
Rail Road Companies, to make an excursion on their roads on 
next Monday ; and the matter was referred to the standing com- 
mittee, to decide on the time and manner of the excursion. 
Mr. James Hall then read a communication, ‘‘on wave lines 
and casts of mud furrows.” 
Mr. Hall presented specimens illustrating a paper read at the meet- 
ing of the Association in Boston, and exhibited some specimens of the 
Medina sandstone, presenting the markings which he called wave lines, 
from their perfect identity with the lines of sand deposited by the re- 
tiring waves upon a sea beach or upon the beaches of lakes.* 
Every one must have observed that each advancing wave carries 
forward upon its crest a small quantity of sand, which at the moment 
of the cessation of the advancing motion, and at the commencement 
of the retreat, is deposited, marking in the most perfect manner the 
outline of the wave. (Mr. H. illustrated by lines on the black-board 
how these might be obliterated by a subsequent wave.) 
These markings, often left on beaches for miles in extent on the 
ebbing of the tide or the dying away of the wind, might appear fanci- 
ful. He supposed that these minute tracings could hardly be preserved 
in the solid strata, but since other markings equally liable to obliteration 
were preserved, there was no reason why these could not be. ‘They 
appear through successive layers of the sandstone, the layers varying 
from half an inch to two and three inches in thickness. 
From the direction of these curves, the wind. must have been from 
the N. W., or varying from that to N. N. W. 
In connection with these markings, were the stranded shells of Lin- 
gula cuneata, which had been drifted ashore, and being an obstacle to 
the retreating waters, they presented all the appearances attendant on 
small pebbles in running streams, where the water scoops out a little 
hollow before it and on each side, while beyond is a little ridge of sand. 
The markings to which the name of mud furrows has been applied, 
consist of little ridges upon the under surface of strata, varying im size 
from the finest possible lines or striz, to that of ridges from an inch to 
six inches in diameter. 
These always occur at the junction of a more sandy stratum with an 
argillaceous one below. 
They have all the appearance of haying been the filling of grooves 
or furrows made in the mud deposit below, after it had become partially 
indurated. No other cause could be assigned for their production. 
* Dr. Mantell in his Geology of the Southeast of England first called the atten- 
tion of geologists ta the occurrence of ripple marks on the sandstones of Tilgate 
Forest. 
