EEV. J. E. CROSS ON THE GEOLOGY OE N.W. LINCOLNSHIRE. 121 



2 & 3, b) is the main representative of the Inferior Oolite in this 

 district, and at first sight might seem to be its only representative ; 

 but I find certain beds at the bottom of this formation differing 

 but little in outward appearance from the rest, yet containing a 

 somewhat different fauna. I have called these, by way of dis- 

 tinction, the Santon Oolites. They show a soft, dark-coloured, 

 ferruginous bed, and an oolitic limestone bed above it. 



The softer bed yields a Belemnite (a rarity in our Oolites), 

 Ceromya bajocciana, Pinna cuneata, Gervillia acuta, Ostrea mima, 

 Hinnites abjectus, Pholadomya fidicula, two Nerincece, two beautiful 

 little Troclii, and one solitary specimen of an Ammonite, thin as A. 

 oxynotus and well keeled, which has been pronounced to be of the 

 family of A. Truellei. The stony bed above yields most of these, and 

 in addition to them, Astarte elegans, pumila, squamula, and minima, 

 Opis cordiformis, Gorbicella complanata, Macrodon hirsonensis, two 

 Cyprince, a large and fine Cardium something like cognatum, and two 

 Trigonice in beautiful preservation (T. hemisplwerica and Phillipsii.) 



"Whatever these beds may represent, I almost fancy that they are 

 dying out here, as I cannot persuade myself that they are altogether 

 continuous, but seem to occur in patches. A little further south, I 

 fancy, they become more permanent. 



Above this lies the Inferior-Oolite stone now often termed Lin- 

 colnshire Limestone, which, with its partings of clay, has an average 

 thickness of 12 yards. One single specimen of an Ammonite, so far as 

 I know, is the only representative of its kind, nay, of all the Cephalo- 

 pods, in this formation. It is of very considerable size, and belongs 

 to the Humphriesianus -group. It is not, I am sorry to say, in my 

 possession. The rest of the fauna corresponds very closely with the 

 lists usually given from these beds in other districts. I may, 

 however, single out for mention the little Rhynchonella Crossii, to 

 which Mr. "Walker has been pleased to append my name, it having 

 been first brought into notice by me. It is a beautiful little shell, 

 seldom exceeding the size of a pea, and filled with pure calcite ; the 

 spines are very thick and strong ; of what length originally, cannot 

 be told ; for, from the hard nature of the matrix, it is impossible to 

 extract them whole ; but they leave a very deep and notable im- 

 pression behind them. Also I may notice a dwarf variety of Trigo- 

 nia Jiemisphcerica, measuring about an inch each way, which is only 

 about half the size this species attains in the beds (just described) 

 below. I am not aware whether this shell is similarly dwarfed in 

 the corresponding beds elsewhere. I should notice also the extreme 

 rarity of Plioladomya fidicula, P. Heraultii being the prevailing 

 species. 



Next above the Lincolnshire Limestone there exists a deep clay 

 (figs. 2 & 3, a), perhaps 40 feet, of a bright green colour in parts, the 

 representative, doubtless, of some member of the Great Oolite series. 

 I have not had good opportunities of observing it ; and its fossils are 

 many of them in very bad condition ; but among them are Ostrea 

 suhrugidosa, 0. Sowerbyi, Gervillia crassicosta, Modiola ungidata, 

 Trigonia flecta, an Icthyodorulite, and fish-palates. 



