Nal. 5S. | JURASSIC OF THE SOUTH WALES DIRECT LINE. 743 
much-jointed beds of massive limestone; the strata are false- 
bedded and wedge-bedded throughout, as well as traversed by 
several master-joints. At all depths in the series the massive 
limestones have a tendency to pass laterally into sandy beds or 
clays, which strike the eye, when viewing the section, as lenticular 
masses embedded in a matrix of jointed false-hedded limestone. 
When standing at any particular point in the cutting, east of the 
tunnel-mouth, it would be easy to exaggerate the stratigraphical 
importance of these clays and sands. For example, in the vertical 
face which contains the mouth of the tunnel, a very conspicuous 
thick band of dark clay is seen at a short distance above the roof 
of the tunnel, resting upon massive limestone-beds which continue 
Fig. 4.—The eastern end of Sodbury Tunnel. 
to the floor, and capped by a prominent sandy bed. Traced later- 
ally however, this clay and its capping of sand die out completely, 
to be replaced by limestones, continuous in all respects with those 
above and below, but containing the same fossils as were found in 
the clay and sand. 
As ancther example, we may take the following 
distance from the mouth of the tunnel, and some 30 feet below the 
clay just referred to, occurs a very characteristic sandy clay, as 
black as coal. Traced towards the tunnel this passes into a brown 
sand, and ultimately into massive limestones; but, under all con- 
ditions, the horizon is well-marked by large specimens of Pholadomya 
daltoidea, which oceur abundantly along ‘this particular level. 
a ———-—_\__ 
ge-bedded = ee 
Eg 
Sa 
> ae 
Upper Great 
Oolite 
Wed 
with Bradford- 
Clay and sand, 
Clay & Great- 
bedded 
Upper 
Great Oolite, Oolite fossils. 
Wedge- 
