﻿122 Revieics — Rev. T. G. Bonne'i/s Camhridgeshire Geology. 



I, CAMBRIDaESHIRE GeOLOGY. A SkETCH FOR THE UsE OF 



Students. By T. G. Bonney, M.A., F.G.S., etc., Tutor and 

 Lecturer in Natural Science, St. John's College, Cambridge. 

 (Deighton, Bell & Co., 1875.) 



THIS sketch of Cambridgeshire Geology is stated in the preface to 

 have been published to give to beginners some information on 

 the local geology of this district. A pamphlet on this subject was 

 privately printed by the late Prof. Sedgwick in 1861. Since that 

 period many papers have been written on the geology of this part 

 of England. Mr. Bonney gives a short account of the strata of the 

 Mesozoic period, and the nature of their variation when traced 

 diagonally across England from the southern counties. The physical 

 geography of the Cambridge district is thus described : " The valley 

 of the Cam is a wide alluvial plain, bounded on the eastern side by 

 a clearly-marked escarpment of the Lower Chalk, on the western by 

 a more irregular hilly district, consisting partly of outliers of Lower 

 Chalk, partly of inferior deposits capped by Boulder-clay. The 

 right bank of the valley is formed by the edge of the great Chalk 

 plateau, which has been corroded by the action of rain and rivers 

 into undulating hills and valleys. From this Chalk plateau sundry 

 streams descend towards the Cam, forming wide valleys with shelv- 

 ing sides, occupied in places by alluvial deposits. The fen land does 

 not extend to Cambridge, its nearest inlets are four to five miles 

 distant ; thence it extends to the sea, as a widespread tract of per- 

 fectly flat land, scarcely above the sea-level." Next follows a descrip- 

 tion of the Jurassic strata, which, in the neighbourhood of Cambridge, 

 consists of a vast argillaceous deposit, with a few local and partial 

 calcareous beds, the lower part of which is Oxford Clay, and the 

 upper part is Kimmeridge Clay ; in some places these graduate one 

 into the other, without any very clear line of demarcation. The 

 lower beds of the Oxford Clay, containing A. Buncani, etc., may be 

 seen at St. Neots ; the higher beds at St. Ives, where the deposit 

 consists of a pale bluish-grey fine clay, with occasional calcareous 

 concretions, crystals of selenite, and lumps of pyrites often altered 

 into limonite. Grypliea dilatata is ver'y abundant, also Am. cordatus, 

 Marice, Eugenii and Hecticus, and Belemnites hastatus. The most 

 important of the calcareous zones is that at Elsworth, described by 

 Prof. Seeley (Ann. and Mag. Nat. Hist. ser. iii. vol. x. p. 98). The 

 Transition Clay has been called by Prof. Seeley Ampthill Clay. Near 

 Upware there is a low broad ridge of Limestone, which Mr. Bonney 

 regards as a representative of the Coralline Oolite. 



The Kimmeridge Clay is best seen at Eoslyn Pit, near Ely. It 

 is of a bluish-black colour, containing Septaria. Among the fossils 

 are Lingula ovalis, Ostrea deltoidea, Exogyra virgida, Am. hiplex, 

 Tngoriellites latus, and several genera of fishes and reptiles. 

 The Neocomian deposits of Potton and Upware are next described. 

 Mr. Bonney adopts the same view with regard to the age of these 



