36S PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [March 12, 



regard to Clay-ironstones, I think they are often due to subsequent 

 changes in the strata : the carbonate of iron having been originally 

 more or less diffused through the silt beds, or shales, has segregated 

 in time, so as to form irregular balls or bands." (I have above made 

 a reservation in the case of concretionary balls.) " But the extreme 

 regularity of many of the bands would lead one to infer that these 

 at least were due rather to deposition than to segregation " *. 



In the Cleveland district the Oolitic ironstones can sometimes be 

 traced to their natural limits. Their structure changes from an 

 oolitic one to a dense compact Clay- ironstone, first in a number of 

 thin beds, which diminish in number till the whole disappears. 

 Thus a bed of inferior ironstone, known as the " top bed," in some 

 places 30 feet thick, is at one place represented by thirty distinct 

 bands of Clay-ironstone in a thickness of 8 feet, whereas a little 

 further north one single bed, 10 inches thick, of a compact Clay- 

 ironstone, is the sole representative of the 30 feet of loose oolitic 

 ironstone further south. A little further north still there is nothing- 

 whatever to represent this bed. These bands appear to me to point 

 to littoral conditions, and to be explained as in the paper. 



Note. — An abstract of the above paper, with much additional 

 matter, was published in ' Iron,' April 26, 1873. 



Discussion. 



Prof. Ansted thought that the explanation offered by the author, 

 though satisfactory for instances of limited thickness and confined 

 area, was not equally applicable to the far larger deposits, such as 

 those in America, extending over hundreds of square miles, and 

 many times as thick as those described. The beds had by some 

 been considered due to segregation subsequently to deposition ; 

 but this view also seemed hardly such as could be generally accepted. 

 The deposits of ironstone varied much in character, sometimes con- 

 sisting of layers of distinct nodules, sometimes of continuous bands. 

 The origin of these two classes appeared to him to have been dif- 

 ferent ; and inj some of the Coal-deposits the ironstone bands were 

 present on a more extended scale than seemed consistent with the 

 author's theory. 



Prof. Ramsay thought that the paper exhibited considerable in- 

 genuity, and that the examples given by the author were intended 

 by him to be equally applicable to large areas. The estuarine cha- 

 racter of much of the Coal-deposits was an acknowledged fact; and 

 the theory proposed by the author was quite in accordance with 

 such a state of things. He did not agree with him that ironstone 

 was never deposited in marine strata, as it occurred in the Yoredale 

 beds and in some Liassic beds. As to the deposits of ironstone in 

 fresh water, he referred to those still taking place in some of the 

 Swedish lakes. 



* ' On the Geological Position and Features of the Coal- and Ironstone-bearing 

 Strata of the West of Scotland/ by James Gh?ilrie, F.E.S.E., p. 14. 



