16 



instances to trace the development of one set of animals from the 

 preceding set. 



Now this regularity prevails with scarcely any break through the 

 whole series of rocks from the Archaean or oldest known beds to those 

 called Tertiary. In all cases we can tell the relative age, the mode 

 of formation and deposition, and the characters of the various kinds 

 of life then prevalent. Tiien suddenly this regularity seems to 

 end, as we come upon a number of s^cattered formations to which 

 the regular laws apparently do not apply, and for a long time the 

 geologists were at a loss to account for this. We rarely find any 

 animal or plant remains m these deposits ; they are not arranged 

 in layers or strata ; they seem scattered promiscuously in various 

 localities, and they repose upon rocks of all ages. All that we can 

 say of them at first sight is, that they are more recent than 

 all bhe rest. At first their apparently confused and disorderly 

 arrangement (if indeed such a term is applicable at all), was taken 

 as proof and consequence of a confused and disorderly period in the 

 earth's history. It was taken for granted that they represented a 

 " great gap separating the present from the past. Some mighty 

 convulsion of nature was thought to have marked the close of the 

 geological ages, and to have immediately preceded the advent of 

 man, and the introduction of the plants and animals with which 

 he is associated." But, says James Geikie, " the study of these 

 deposits has unfolded a deeply interesting and almost romantic 

 history. We are introduced to scenes that are in strangest 

 contrast to what now meets the eye in these latitudes ; geological 

 and physical changes of the most stupendous character pass before 

 us ; vve see our islands and northern Europe at one time enveloped 

 in snow and ice, at another time well wooded and inhabited by 

 rude tribes of men and savage animals ; now the British islands 

 are united to the continent, — again, the sea prevails, and a large 

 part of Britain is overwhelmed beneath the waters of the ocean, 

 across which ere long float rafts and bergs of ice. To these suc- 

 ceed vast confluent glaciers which overflow a large portion of the 

 British area, and usurp the bed of the sea. Yet again, we beho]d 

 the great icefields vanish away and Britain once more becoming 

 continental and re-peopled. Finally, we follow the working of 

 those physical influences, by which at last the present order of 

 things is brought about." In fact, we may say that what seemed 

 a puzzle at first, has now become a key to at least one chapter in 

 ancient history. 



Let us see then, what are the characters of these deposits from 

 which such a romantic history has been extracted ? There are 

 three : — Their apparently disorderly distribution, their varied 

 composition, the stones and blocks of all sizes contained in them 



