228 PROCEEDINGS OE THE GEOLOGICAL SOCIETY. [Feb. 5, 



ampton Sand, those which define the separation of the Middle from 

 the Upper Division everywhere obtain ; for the presence of the 

 sand-bed (generally with its characteristic vertical plant-markings, 

 and designated by Mr. Judd the " Lower Estuarine Series ") is 

 observable wherever the Northampton Sand and higher beds are 

 found in the same section. 



It is a question, therefore, whether it would not be wise to 

 abandon the hard line of separation between these Middle and 

 Lower Divisions, and to class them together as the " Ferruginous " 

 or marine beds of the Northampton Sand, retaining the distinction 

 of the Upper Division of that formation under Mr. Judd's name of 

 the " Lower Estuarine Series." 



Exception has been made to the use of Mr. Judd's terms " Upper 

 Estuarine " and " Lower Estuarine." I shall not enter upon this 

 question : Mr. Judd is well able to maintain his own position. But, 

 as these terms have been adopted in the maps of the Geological 

 Survey, and will doubtless also be used in Mr. Judd's forthcoming 

 Memoir, I have deemed it well, for the avoidance of confusion, to 

 retain them in this treatise. For the same reason, I have adopted 

 Mr. Judd's term of the " Great Oolite Clay " for the clay overlying 

 the Great Oolite Limestone. 



It is a fact worthy of notice that the two series of beds, the 

 " Upper Estuarine " and the " Lower Estuarine," — so widely sepa- 

 rated in time and character, the one belonging to the period of the 

 Great Oolite, and the other to that of the Inferior Oolite, — occur 

 together in vertical juxtaposition in the neighbourhood of North- 

 ampton, throughout a large district including parts of both divisions 

 of the county, and in Oxfordshire. In the latter county, the 

 Upper Estuarine is traceable through to the Stonesfield Slate-bed ; 

 and the difficulty of separating the two Estuarines in Oxfordshire 

 led to the conclusion arrived at, and published by the Geological 

 Survey in 1860, that the Northampton Sand (few of its fossils being 

 then known) was equivalent to the Stonesfield Slate. 



An earlier conclusion prevalent among geologists (and perhaps 

 still retained by some) was, that the Great Oolite limestone of the 

 high grounds of the Northampton district, was identical with the 

 limestone (the Lincolnshire Limestone) which occurs between Ket- 

 tering and Stamford, and, characterizing the country about the 

 latter town, extends on through Rutland and Lincolnshire into 

 Yorkshire ; that this Limestone was a member of the Great Oolite 

 series ; and that the calcareo-arenaceous slate of Collyweston and 

 Easton, which bases this limestone, was the equivalent of the 

 Stonesfield Slate of Oxfordshire : and this opinion has been main- 

 tained notwithstanding the discrepancy indicated by the very dis- 

 similar fossil contents of the two formations and by the anomaly 

 of their relative stratigraphical position. 



I hope to be able to show the distinction between these two 

 formations ; to demonstrate, from the succession of beds at different 

 points between Northampton and Stamford, and in the districts 

 about Stamford, that, while the position of the Northampton Lime- 



