472 Reports and Proceedings — 



are disposed to "strain at a gnat and swallow a camel" that this is a condition of 

 original deposition. Fortunately there is a fine series of the shells of Mollusca in 

 these beds, which have undergone a similar change, and are almost wholly con- 

 verted into Spathic iron. The legitimate inference is that a salt of iron has 

 replaced a salt of lime wherever the latter was present in the rock. Some are not 

 satisfied with this explanation because they do not exactly see what has become of 

 the lime. Such objectors might study the history of pseudomorphic action, as 

 exhibited from the earliest times, with advantage. The source of such vast 

 quantities of iron is a far more obscure question '. but as the iron undoubtedly is 

 there now, whether it arrived by deposition or replacement matters little. It must 

 be borne in mind that most, if not all, of these Oolitic ironstones, either in York- 

 shire or Northamptonshire, are overlain by porous sandy beds, which frequently 

 contain considerable traces of carbonaceous matter. This probably is but a 

 vestige of what once existed in the peaty beds accompanying "Estuarine" con- 

 ditions. Layer after layer of micaceous sands, rich in iron, have been permeated 

 by organic acids, the products of the decomposition of these vegetable masses, 

 wlrich, attacking the mica and any such basic minerals which might be present, 

 removed their more soluble constituents, and thus by perpetually exhausting the 

 sands, left those bleached and partly coherent masses which so often overlie the 

 ironstone beds. This is p'robalaly one source of the iron ; as the solution, origin- 

 ating in the manner described above, and the ' ultimate decomposition of which 

 would most probably i-esult in the formation of carbonates, might possibly, in the 

 presence of an excess of carbonic acid, decompose and replace any porous lime 

 carbonates they might meet with in their descent. The presence of an impemous 

 bed of clay at the base of such rocks would materially facilitate the operation, by 

 keeping the original Oolite in a sort of bath, containing a solution of the replacing 

 salt : though, of course, the hydrostatic pressure of the water would ultimately 

 force the solution containing the extruded mineral to find an exit somewhere along 

 the lines of least resistance ; or it might be removed by simple diffusion in cases 

 where the pressure was equal on all sides. The Yorkshire Oolitic Ironstones 

 remain carbonates still in many cases, probably because they have a great mass of 

 rock above them. Those in Northamptonshire have undergone a second chemical 

 change, principally from the action of oxygenated waters ; which have had the 

 curious effect of producing a sort of centrifugal motion of the resulting oxide, 

 which enables the owner to get rid of a good deal of foreign matter by the simple 

 process of sifting. 



The last place visited was Watkins Brick-pit, where the Upper Estuarine clay 

 is capped by a few feet of Great Oolite ; close t)y is a pit of Lower Estuarine, 

 separated from the Upper by a ferruginous band, not observed on this occasion. 



Mr. Sharp then conducted the party to Dallington-hall, where he and his family 

 most hospitably entertained them. The rest of the evening was spent in inspecting 

 Mr. Sharp's magnificent collection of local fossils. 



On the following day, an early start was made by train for Stamford, about 40 

 miles distant. The line runs due north as far as Market Harborough, through an 

 undulating country, chieily in the Upper Lias, yielding no good sections by the 

 way. A sort of escarpment of the Northampton Sand flanks the route on the east, 

 as far as Maidwell, where the first indications of the Lincolnshire Limestone 

 appears. In this neighbourhood the country is extremely fertile and beautiful. 

 All this wealth of soil must be due to the mixing of the rich clays of the Upper 

 Lias with the sands and calcareous matter derived from the destruction of the 

 once overlying beds. From Market Harborough to Stamford, the mean direction 

 of the route was N.E., and chiefly along the Welland Valley, which is flanked on 

 the S.E. by a fine escarpment, capped by the Lincolnshire Limestone, on the edge 

 of which Cottingham, Rockingham Castle, and Gretton are commandingly perched. 



At the Stamford Station, Mr. Sharp drew attention to the great dislocation 

 which has occurred on the south side of the Welland Valley, and which may be 

 partly traced in the railway cutting. The general effect of this dislocation is to 

 divide the Inferior Oolite beds of St. Martin's from those at the top of the hill on 

 the London-road, a mass of Upper Lias being wedged in between them. This 

 was also observed as the party ascended the hill towards Lord Exeter's Ironstone 

 Quarries, which were visited, as also a quarry for road metal, where the party first 

 made the acquaintance of the Lincolnshire Limestone, here a pale-coloured Oolite, 



