Preface. ix 



owe to Mr. Etheridge and Mr. Sharman ; to the first 

 for much valuable information concerning the organic 

 relics of each formation, and also for the plan of each 

 of the sets of figures engraved as illustrative of the for- 

 mations, every one of which may be considered as more 

 or less typical of the strata or groups of strata referred 

 to in the text, in which, however, all of the fossils 

 figured are not always named. . Mr. Sharman executed 

 the drawings of these fossils with his accustomed skill 

 and accuracy. 



I have also added some landscapes. One of these, 

 the Pass of Llanberis, fig. 86, is reduced from a coloured 

 crayon drawing by Mr. Gillespie Prout, and fig. 87 is 

 taken from a photograph. The original of fig. 88 was 

 drawn by the late Sir Henry De la Beche, and fig. 89, 

 with the dwindling ice entering the lake, is the repre- 

 sentation of an episode in the history of the glacier, 

 supposed and drawn by myself. The blocs perches of 

 fig. 90 was drawn by the late Professor Edward Forbes. 

 All of these were originally published in my paper on 

 'The Old Glaciers of Switzerland and North Wales.' 

 The Gorge of the Avon is from a photograph. All the 

 other landscapes, excepting one from my 6 Geology of 

 Arran,' have been engraved directly from drawings, as 

 they were roughly done in sepia and pencil in my geo- 

 logical note books, and, together with the sections and 

 other illustrations, many of them new, they are intended 

 to bring before the eye the meaning of various theories 

 propounded in this work, by help of which, anyone, 

 by a moderate exertion of thought, may realise the 



