240 MR. L. t). STAMP ON THE HIGHEST [vol. lxxlv, 



faults of the district. There is also a system of folds with axes 

 approximately east and west, and at least one important fault runs 

 a few degrees south of east to north of west. It probably extends 

 for some distance westwards up the Redlake Valley, but there is 

 entirely hidden by alluvium. 



Jointing is well developed, especially in the Mhynchvnella and 

 Chonetes Beds. 1 The two principal directions are parallel to the 

 two series of faults, and the jointing was obviously developed during 

 the folding, as the inclination of the joint-planes to the vertical 

 varies with the dip, but to a less extent. 



VI. Summary and Conclusions. 



The period of transition from Silurian to Old Red Sandstone 

 times was one of violent earth-movements and volcanic upheaval in 

 many parts of Great Britain, and a great unconformity separates 

 the rocks of the later system — laid down in land-locked seas under 

 continental conditions — from the fossiliferous marine rocks of the 

 earlier. In that part of the country which is now occupied by 

 South-East Shropshire, however, the transition was most emphatic- 

 ally a gradual one, and the change in the character of the rocks can 

 be traced step by step. 



During the tranquil Salopian period a great thickness of 

 monotonous grey sediment was laid down. Perhaps the first sign 

 of a change in conditions and a shallowing of the sea is the increased 

 number of fossils in the upper part of the Lower Chonetes Beds. 

 The flagstones of the Upper Chonetes Beds have (as mentioned above 

 on p. 230) an undulating surface due doubtless to wave-action, and 

 this points to a further shallowing of the sea. The bands of fossils 

 of small individuals and the Ludlow Bone-Bed farther east indicate 

 the commencement of conditions unfavourable to the marine fauna 

 which had hitherto flourished. Later the increasing concentration 

 of iron salts in the water caused the slightly-greenish tint of the 

 Upper Chonetes Beds. A shallow-water fauna of gasteropods and 

 Lingulce gradually replaced the familiar forms of the Chonetes 

 Beds, as, for example, Chonetes, JRhy?ichonella,and Orthis, and the 

 occurrence o£ I* latysc his ma bands shows how well this fauna flourished 

 for a short time during the deposition of the Platyschisma Shales. 

 Then sediments of a very different nature were deposited : micaceous 

 sandstones in place of calcareous silts. The succeeding Temeside 

 Shales have many features in common with sediments of other ages 

 which mark the commencement of arid conditions. Among the 

 characteristics may be mentioned the green colour, the rubbly 

 and marly nature, and the scanty fauna including ostracods 

 (Leperditla and Be//richia),snid stunted lamellibranchs. Finally, 

 even these few organisms died out and the succeeding rocks (Old 

 Red Sandstone?) 3 assumed a red colour, since the natural process 

 of oxidation of the iron salts was not hampered by the presence of 

 decaying animal tissues. 



1 See R. I. Murchison, ' Siluria ' 4th ed. (1867) p. 131. 

 8 See note, p. 242. 



