84 Reviews — P rest wick's Geological Text-Book. 



acting on the surface of the globe, in so far as they are of a nature 

 to furnish evidence which may assist in the interpretation of the 

 mode of formation of the sedimentary strata, of the disturbances to 

 which these strata have been subjected, and of the succession of life 

 of which they contain the remains." 



Then we have Bain treated as a geological agent ; the formation 

 of Deltas, their age ; River Denudation ; the formation of Valleys ; 

 Drainage-Influences ; the Canons of the Colorado, — illustrated by a. 

 page-cut of Marble-canon and a glimpse at the Dolores canon. 



From this we pass to the consideration of Marine Action, — the 

 origin of the coast shingle in the English Channel — illustrated by the 

 famous case of the Chesil Bank — and the cause of the wear of coasts, 

 illustrated by the gradual destruction of Luncly Island, an 'outlier' 

 of the old North Devon Coast, the Chalk Cliffs of Brighton, 

 Dover, etc. 



In Chapter VII. the subject is continued, and we are invited to 

 consider waste (by chemical solution) in the soluble matter carried 

 down to the sea and into lakes by Bivers; its character and quantity; 

 and the resultant formation of Calcareous strata. 



The Organic origin of Limestones is next touched upon, and the 

 presence of soluble silica inCretaceous and Jurassic strata is adduced as 

 evidence that a very different state of things existed then, to anjr which 

 obtains in the present seas. May not the soluble silica referred to 

 have been very largely derived from the subsequent decomposition of 

 the vast numbers of siliceous sponges which are known to have 

 existed in the seas of the Secondary period ? and may not these 

 chemical changes have taken place long after the Calcareous muds 

 forming the sediments of these Mesozoic waters had been ac- 

 cumulated and to a great extent solidified ? 



The author refers to the various modem Calcareous beds now 

 forming, such as the shell-limestones accumulating along many 

 coasts like that of Guadaloupe, the Canaries and the Island of 

 Ascension. He next glances at Deposits in Lakes, of which the 

 shell-marls always form a most interesting series, often rich in 

 organic remains. 



From these the author passes on to consider those strata which 

 owe their present state to subsequent chemical reaction, such as 

 Magnesian Limestone, Gypsum and Bock-salt. 



Space does not permit us to dwell longer on this interesting work. 

 The seventeen chapters that follow are not merely a bare compila- 

 tion from the works of other observers, but Brof. Brestwich is able 

 to bring much of his own original labours in the past to bear upon the 

 subjects under consideration, and so to exalt the work into a far 

 higher position than that of an ordinary text-book. 



We hope to come back to its consideration at a future day. A 

 most valuable feature of the book is its excellent Index of 27 pages, 

 of three columns to a page, which renders the contents easily 

 accessible to all, and gives the book a very high place as a work of 

 ready reference. 



