O INTRODUCTION. 



its more massive facies, was formed very far from land, 

 though the water was doubtless clear and deep in those 

 places where it attains great thickness. 



Deep-water Beds. It is now generally acknowledged 

 that the great mass of the rocks which compose our 

 modern continents are such as are now only formed within 

 200 or 300 miles of land, and very seldom include any 

 deposits which resemble those now accumulating in the 

 depths of the Atlantic and Pacific Oceans. There is only 

 one formation in Britain which was undoubtedly accumu- 

 lated in deep water at a great distance from land of a 

 continental character, and that is the Chalk. When, there- 

 fore, we speak of deep-water beds, it must be remembered 

 that comparatively deep water is meant, and not water of 

 oceanic depth. 



Massive compact limestones and calcareous clays or 

 marls have generally been formed in water of considerable 

 depth. Many bluish and greenish clays, shales and slates, 

 especially such as do not contain many fossils, have doubt- 

 less been formed in deep water, and are comparable to the 

 blue and green muds which are found over certain tracts 

 of the sea bottom, between the shallow water and the 

 deeper tracts of the ocean. 



Variations in Thickness. The evidence derivable from 

 the thinning and thickening of deposits also merits some 

 examination. If we consider the case of sediment which is 

 being transported by the action of a current setting off a 

 coast-line, there can be little doubt that the greatest 

 amount of sediment would be thrown down at a certain 

 distance from land, where the bottom began to shelve 

 into deep water. Little could be deposited in the shallow 

 water near shore, but would be carried to a greater or less 

 distance in proportion to the depth of the water ; and if 

 the bottom shelved gradually the deposit might cover a 

 considerable space, .but as soon as fairly deep water was 



