THE CORNSTONES OF HEREFORDSHIRE AND 

 MONMOUTHSHIRE. 



By Db. M'CULLOUGH, President. 



Although the Old Red Sandstone or Devonian System, as developed in 

 this and the adjoining counties, does not prfisent those great masses of limestone 

 which characterise many other formations, yet lime is very generally distributed 

 throughout the various deposits forming that great system. Besides a consider- 

 able portion being present in many of its sandstones, and in its clays or marh, 

 it is often deposited as limestones, which are usually more or less impure from 

 admixture with other minerals, chiefly sand and clay. These limestones may 

 be divided into two classes. In the first, the lime is deposited in nodules or 

 concretions, the intervals between the nodules being filled up by matter less hard 

 and calcareous than the concretions themselves, so that the mass is easily 

 separated into its component nod\iles. In the second class, the cementing mate- 

 rial is often more calcareous than the particles cemented together, forming a 

 hard coherent band or stratum, after assuming somewhat the character of a 

 conglomerate. The former, or concretionary limestone, is well developed in this 

 neighbourhood, and excellent opportunities exist for examining it at the 

 numerous quarries where it is worked either for burning or for road stone. It 

 is found in beds of varying depth, the thickest which I have been able to examine 

 being from nine to ten feet. Sometimes these beds are immediately overlaid 

 by a stratum of sandstone, and sometimes they pass gradually into a bed of 

 superincumbent marl. Besides these great beds, concretionary limestones are 

 found in thinner bands of one or two feet imbedded in clay in the form of marl, 

 and frequently a single row or course of concretions is found imbedded in the 

 marl, much as a row of flint nodules is seen in chalk. Very often the beds 

 of marl contain numerous small limestone nodules distributed through them 

 without any apparent arrangement. 



The second class is very different, and presents many varieties. Most of 

 them contain a greater mixture of other minerals than does the concretionary 

 form ; the calcareous matrix cementing together not only calcareous nodules, 

 but also portions of sand and clay, and they vary in texture from a tolerably 

 compact and fine grained stone up to a rather coarse conglomerate. They 

 vary in thickness from an inch or less up to 14 or 15 feet, which is the greatest 

 depth I have observed. Many of them are very hard and durable, and are used 

 as coarse building stone, and some of them are valued as road stone. They 

 are quarried chiefly for the latter purpose, and to this the geologist owes many 

 opportunities of examining them. 



I have said that these deposits, regarded as limestones, are more or less 

 impure. The degree of impurity, however, varies constantly, not only in 

 different beds, but in different nodules of the same bed, and even in different 



