ON EXCAVATIONS IN THE PALEOZOIC ROCKS OF WALES, ETC. 117 



' badly preserved brachiopod which suggests Orthis lenticularis,' no 

 fossils were discovered. 



The total thickness of the Shoot Bough Road shales cannot be safely 

 estimated, owing to want of artificial exposures between the excavations 

 described, but the mapping of the surface indicates a very considerable 

 thickness, amounting to some 300 to 500 feet, or possibly more, for the 

 whole" group. 



B. — The Excavations near Bobin's Tump. 



Bobin's Tump, viewed from the north, is a small conical hill about half 

 a mile to the south of the Comley Quarry. It is in the line of, and has 

 the appearance of being a continuation of, the Hill House Bidge, but, 

 geologically, it is very different, and the two features are severed by a 

 somewhat flat area occupied by two fields. The summit rises to about 

 990 feet and is oval-shaped, with a length of about £0 yards in a north- 

 east and south-west direction. It is connected with the higher 

 (Ordovician) ground at the foot of Caradoc Hill by a saddle some 40 or 

 50 feet lower in elevation. Several natural exposures of grits and sand- 

 stones are to be seen on the summit, but no details of the succession 

 were visible without excavation. A little stream descending from the 

 lower slopes of Caradoc Hill has cut a deep trench along the north-west 

 side, and here there are isolated natural exposures of rather soft greenish 

 and reddish micaceous sandstone of the type of the Lower Comley 

 sandstone, and characterised by burrows and tracks of organisms. 



Excavation No. 28, on the Saddle. 



Near the place marked 2S, trials were made on the Saddle at four 

 spots, all of which showed green micaceous sandstone with a fairly 

 regular north and south strike and a dip to the east of about 45°. The 

 sandstones vary in hardness from point to point, but are otherwise 

 uniform in character, and are evidently part of the series exposed near 

 the stream. 



Excavations No. 29, summit of Robin's Tump. 



A series of excavations were made in connection with the natural 

 exposures of the summit. These are too close together to be shown 

 separately on the map. 



No. 29a, situated on the northern shoulder where there was a 

 small natural exposure of much weathered rock, shows about 4 feet of 

 well-bedded coarse calcareous and conglomeratic grit, with many ferru- 

 ginous casts of fragments of trilobites and grains of bright green 

 glauconite, exactly recalling the conglomeratic portion of the Quarry 

 Bidge grits. The dip is about 45° to a little south of east. Below 

 this conglomeratic bed some 3 or 4 feet of a strong, green, micaceous 

 sandstone are visible, the beds of which dip at a rather steeper angle 

 decidedly north of east. From the solid rock immediately touching the 

 overlying conglomeratic grit I obtained two specimens of cavities, pene- 

 trating the sandstone in a curvilinear manner. They are somewhat 

 quadrangular in section, 15x20 mm. in diameter, have well-defined 



