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THE OLD RED SANDSTONE OF HEREFORDSHIRE. 



By Rev. W. S. Symonds. 



The series of stratified deposits which occupy the greater part of this County 

 is called the Old Red Sandstone, or Devonian group, and lies between the Silurian 

 and Carboniferous strata. At the close of the long Silurian period, a great change 

 occurred in the character and colour of the deposit, over large areas of those primeval 

 seas. We find the gray mud of the Upper Ludlow rock succeeded by red sediments, 

 and this red colour is owing to the influence of iron oxides. Whole tribes and 

 families, with which we are familiar in the Sikirian beds, perish and disappear, 

 and the tenants of the deep, whose records we have traced amongst the limestone 

 and mudstones of the upper Silurians, pass away for ever, and scarcely a species 

 of the Old Red Sandstone group, in whatever part of the world it has been 

 examined, is identical with the creation which rests below. 



A careful investigation of the thickness of the Old Red Sandstone, by Sir 

 Roderick Murchison, and the Government Geological Surveyors, gives its enor- 

 mous depth at not less than 8,000 to 10,000 feet. It was originally divided by 

 Sir Roderick into three groups of deposits : (i) a quartzose conglomerate passing 

 downwards into (2) chocolate, red, and green sandstone, and marl ; and (3) the 

 tilestones. It is now however ascertained, that this lower or tilestone division 

 penetrates rather to the Silurian rocks, for the fossils agree in general character 

 with those of the Upper Ludlow which lie immediately beneath. The Cornstone 

 group, with its many unregular courses of mottled red and green earthy limestones, 

 is the true Old Red deposit which succeeds the tilestones, and these are more 

 especially the beds which we have journeyed to investigate this day. 



Far above our heads, however, in by-gone periods of our planet's history, 

 there existed upon this Cornstone group the upper quartzose conglomerate No. 

 I. Enormous denudation and excavation have long since borne away every 

 particle of these upper beds from this district. 



I had the pleasure of examining their contemporaries and equivalents on 

 the sides of the Blorenge some months since, in company with several members 

 of this Society, and it may not be uninteresting if I allude to our observations. 

 The pleasant town of Abergavenny, surrounded as it is with picturesque hills 

 all exhibiting the immense development of the Old Red Sandstone, was our starting 

 point. We were met at the station by our hospitable entertainer and lately 

 elected member, Mr. Elmes Y. Steele, and with our Honorary Secretary (Mr. Suter) 

 for our guide we commenced the examination of the Blorenge. 



The valley of the Usk is a great line of fault, caused no doubt by intense 

 earthquake action that succeeded the Coal period, when the thick floor of the 



