2 INTRODUCTION 



some descriptions of geological phenomena, and sound inferences 

 were sometimes drawn from the facts. But no attempt was made 

 to gather an extensive series of observations, or to construct a har- 

 monious system of facts and inferences, and no one imagined that 

 a connected history of the earth was within the bounds of human 

 attainment. Before such a history could be written, it was neces- 

 sary that the other physical and natural sciences should have 

 reached a considerable degree of perfection ; for geology, as we 

 have seen, is a synthesis of these sciences. It was only in the latter 

 part of the eighteenth century, that these other branches of know- 

 ledge had so far been perfected that they could offer to the geolo- 

 gist a firm foundation upon which to build the structure of his 

 own science. The early workers in geology hardly attempted 

 more than to ascertain the materials of which the earth is com- 

 posed and the way in which those materials are put together. In 

 carrying out this apparently simple task, it soon became evident 

 that the present condition of the earth is the outcome of a long 

 series of past changes, which must be understood if we would 

 comprehend the earth's structure as it is now. The past must be 

 studied in the light of the present, and the present in the light of 

 the past, for each supplements and helps to explain the other. 



Such a conclusion is repugnant to our instinctive feeling, that the 

 earth is stable and well-nigh unchangeable, a feeling which finds 

 expression in Bryant's familiar line : " The hills rock-ribbed and 

 ancient as the sun." This very natural belief is due to the exceeding 

 slowness with which the surface features of the globe are modified, 

 so that in the brief span of human life the modifications are almost 

 imperceptible. Generations of men live and die in the same spot, 

 while the natural features of hill and rock, valley and plain, seem 

 to remain exactly as they were. When, however, attention was at 

 last directed to these changes, it was found that they were unceas- 

 ing, and were especially noticeable in lands which, like the coun- 

 tries around the Mediterranean, had been occupied for many 

 centuries by civilized men. Occasionally, too, great tempests or 

 earthquakes or volcanic outbursts produced changes which could 

 not but strike the most careless observer. 



