TRANSACTIONS OF SECTION OC. 505 
mantle over the land which prevents the wind from picking up the lighter 
material trom below, which they protect. It is only those stones on the surface 
that are wind-etched or show the faceted form, These gravels were deposited 
during the pluvial period, immediately preceding the present arid one, and there- 
fore it would seem that the only reliable test to prove that a deposit was a desert 
formation would be to find in it tetrahedral and wind-etched stones. 
2. Fifth Report on the Fauna and Flora of the Trias of the 
Lritish [sles —See Reports, p. 298. 
3. On the Structure of the Mandible in a South African Labyrinthodont. 
By Professor H. G. Srexey, 7.2.5. 
The specimen was found by Mr. Alfred Brown at Aliwal North and presented 
to the British Museum. It is a segment from a ramus indicating a skull about 
2 feet long, and at the transverse fractures shows the Meckel cartilage cavity and 
the bones around it. ‘There are two external bones—the dentary, which carries 
large teeth in shallow sockets, and parallel to it is the infra-dentary. This 
element, found in certain fish, has not been observed before in Labyrinthodonts. 
On the inner side of the Meckel cartilage are two bones: one of these is seen 
externally on the base of the jaw, and regarded as the angular bone. Above it is 
the surangular bone, which carries a row of teeth rather smaller than those in the 
dentary bone. On the inner side of the jaw is the splenial bone, which hides the 
suture between the angular and surangular bones. The teeth are solid and have 
a relatively simple labyrinthic structure. The fragment shows that with the 
coronoid and articular bones the mandible may include seven elements on each 
side or more. 
4. The Origin of the Upper Keuper of Leicestershire. 
By T. O. Boswortn, B.A., F.GS. 
The Condition of the Rocks beneath the Keuper.—The Charnian igneous rocks 
beneath the Keuper are comparatively fresh right up to their surfaces, but where 
the marl has been denuded and the rocks are exposed to the present climate they 
are decomposed, 
The Surface Features of the Rocks beneath the Keuper.—Smoothed, fretted, 
and curiously carved surfaces are seen at Mount Sorrel,! Croft, Sapcote, Groby, &e., 
and usually wherever the marl rests on igneous rocks, They are often pitted and 
sometimes highly polished (e.g., at Narborough). But where the rocks are cleaved 
or broken, as at Swithland and Bardon, the floor beneath the Keuper is rough and 
craggy. 
The Nature of the Deposits—Everywhere the beds dip in the direction of the 
surface slopes on which they lie, and the amount of dip depends upon the steep- 
ness of the slope. Catenary bedding is seen at Croft and Groby. Near the rocks 
the marl contains grit and stones, and there is generally a breccia at the base. 
The stones are of varied sizes, sometimes worn and sometimes very angular, 
They are in a remarkably fresh condition. 
Both stones and grit are derived entirely from the particular rocks which the 
beds containing them surround. In these beds there is often a small amount of 
quartz sand, sometimes apparently wind-worn. It yields the same heavy minerals 
as the ‘ Upper Keuper Sandstone.’ 
In many cases-—e.g., around the S. Leicestershire igneous rocks—this sand cannot 
be of local origin. 
At Croft some of the Upper Keuper Sandstone consists of almost spherical 
grains, and appears to be a desert sand. 
' Prof. Watts, Geographical Journal, June 1903. 
