TRANSACTIONS OF THE SECTIONS. 93 
substance ; and the amount of absolute compression when the cleavage was developed, 
as deduced from the form of the green spots, indicates that the amount of water 
squeezed out was almost exactly the same as is requisite to render clay quite plastic. 
The other extreme structure is a cleavage due to very close joints, often so close as to 
be quite undistinguishable unless a thin section is examined with the microscope, 
whilst the arrangement of the particles in the spaces between them is independent of 
the direction of the joints, and is often related to quite another plane. This kind of 
cleavage may therefore be called close-joints-cleavage ; and agrees with what experi- 
ment shows would have been the result if the rock had yielded to change of dimen- 
sions like a rigid body, by the formation of close cracks, These two kinds of cleavage 
obey materially different laws; but at the same time, in like manner as there is a 
gradual passage from rigidity to plasticity, so there is also between these two kinds of 
structure, due to the rocks yielding in one way or the other according to the cireum- 
stances of the case; and thus the structure affords an indication of the actual condi- 
tion of the rocks at the time when they were compressed; and perhaps also, in some 
cases, indicates whether the movements of elevation were sudden or gradual. 
The paper concluded with a list of the various physical structures the author had 
met with in stratified rocks. A difference in the kind of chemical change that has 
occurred, and the previous or subsequent action of mechanical compression, when the 
rocks were in a condition to yield as plastic, flexible, or rigid bodies, have produced 
many more distinctly different structures than has been usually supposed. 
On a Fossil of the Severn Drift. By the Rev. W. S. Symonps. 
The excavations of the alluvial drift of the Severn at Tewkesbury Ham are nearly 
40 feet deep, and the river-bed itself has been dredged to the depth of 7 feet. The 
river-bed contains osseous relics of the human race several feet below the surface of 
the gravel; these are associated with the remains of Roman pottery, the vertebra of 
a whale, and many singular round-shaped glass bottles of great thickness. The allu- 
vial drift is a mass of clay and brick earth, 39 feet thick, resting upon an ancient 
river-bed of gravel and shingle, and about 374 feet from the surface we find the fos- 
silized antler of a large stag (Cervus). ‘his antler is at the base of the brick earth, 
a few feet above the gravel. I was interested in observing the difference in the state 
of fossilization between the vertebra of the whale, which is little altered, and the antler 
of the deer, which is nearly stone. The antler is in much the same state as those 
mammalian remains discovered by Mr. Strickland in the drifts of Avon Valley ; while 
we may compare the vertebra of the whale with the large crooked-horned head of a 
Bison, obtained by Mr. Strickland, sen., from the Avon river-bed. From comparison 
of the fossils, I am inclined to believe that the cervine antler of the Severn is the 
relic of an animal that lived in the period of the Bos primigenius, a fine skull of 
which is in Mr. Strickland’s possession. 
On a New Species of Eurypterus from the Old Red Sandstone of Hereford- 
shire. By the Rev. W. S. SyMonps. 
This fossil was discovered by the parish clerk of Rowlstone, Herefordshire, and pre- 
sented to the Rev. W. Wenman. Mr. Symonds examined the correlation of the rocks 
in which this fossil was found, and stated that they were grey sandstones of the upper 
Cornstones, and pass upwards into those red and chocolate-coloured sandstones which 
are surmounted by the “‘ Old Red conglomerate.” The Eurypterus is a Silurian fossil 
of the Lower Tilestones, found by Mr. Banks associated with Pterygotus, Pteraspis, 
- and Himantopierus at Kington, and again in the Upper Tilestones of Kidderminster, 
_by Mr. Roberts, with Cephalaspis Lyelli, Parka decipiens, and Pteraspis truncatus, 
“ Eurypterus pygmeus”’ is found with the Lingula cornea, but the large form of that _ 
crustacean, now about to be described by Mr. Salter, is a different and entirely new 
- Species. 
On the Geology of the Galty Mountains, Sc. 
By A. B. Wynne, Geological Survey. 
The author presented a north and south section across the summit of Galty More 
