156 



A T) D E E R R 



[By the Rev. Wu.liam I'^ijiot, President.] 



In attempting to interest you in the geology of the district through which our 

 excursion of to-day has led us I should premise that I am net speaking of any 

 knowledge of that particular district which I myself have gained at first hand. 

 Such acquaintance {the truesfand only complete acquaintance) with the great system 

 of rocks over a portion of which we have passed as can be made by labour in the 

 field and with the hammer I have had little opportunity of cultivating, and that 

 not in this county. My remarks are gathered, therefore, from various writers 

 learned in the subject, and, with respect to them, if the poetic comparison be not 

 too ridiculously daring, considering the character of my composition, I might say, 

 as I think it is Montaigne who somewhere says, that I have cidled a nosegay of 

 flowers, and only the string that binds them is my own. 



You are, of course, generally aware that the rocks immediately beneath our 

 feet at this moment, are a portion of that well marked formation which is known 

 as the Old Red Sandstone, in contradistinction to those of a more recent origin 

 which are called the New Red Sandstone. Its maximum thickness is estimated 

 at about 10,000 feet. It is composed for the most part of red, grey, and sometimes 

 yellow sandstone, with beds (as we reach the upper limits of the system, or in 

 other words those last deposited,) of conglomerated pebbles, in many instances of 

 large size, while here and there, as I shall have occasion to notice more particularly 

 just now, there occur bands of impure earthy concretions of limestone, which are 

 technically called Cornstcnes. The varying colours of the deposited sands, from 

 the bright red, that gives its name to the formation, to the sort of cream coloured 

 yellow to be seen in the neighbourhood of the Clee hills, are due to peroxide of 

 iron with which the waters that deposited them must have been heavily charged. 



In point of geologic order the Old Red Sandstone occupies a middle position 

 between the ancient rocks of the Silurian system and the Carboniferous, or coal 

 bearing, deposits. We observe the beds of the former passing beneath these 

 sandstones, while they in turn are overlaid by the limestones and coal measures of 

 the latter. And, occupying this position, they mark a very distinct epoch in the 

 histciry of life upon the globe. Different species of shells, even if of the same 

 genera to those found in the Silurian rocks, appear. Some of the most marked 

 inhabitants of the older seas, the trilobites, become exceedingly scarce, and their 

 place is taken by multitudes of fishes, of which only a few are to be found in the 

 uppermost beds of the Silurian. Some of these fishes have their representatives 

 in existing waters, and the familiar lobster is a sort of far ofif cousin of the large 

 crustaceans who have left their remains embedded in these stones. To give you 

 an idea of the number and variety of these denizens of the Old Red deeps, I may 

 say that of one group of fishes alone,— the Placo ganoids as they are called— no 

 less than 113 or 114 species have been found in rocks of this and the contempo- 

 raneous Devonian age. On the other hand, although in the lowest or first 



