414 SIR CHARLES LYELL 



where to demonstrate, 1 it may be well to allude to them 

 briefly in this place. 



The first and greatest difficulty, then, consists in an ha- 

 bitual unconsciousness that our position as observers is 

 essentially unfavourable, when we endeavour to estimate the 

 nature and magnitude of the changes now in progress. In 

 consequence of our inattention to this subject, we are liable 

 to serious mistakes in contrasting the present with former 

 states of the globe. As dwellers on the land, we inhabit 

 about a fourth part of the surface; and that portion is 

 almost exclusively a theatre of decay, and not of reproduc- 

 tion. We know, indeed, that new deposits are annually 

 formed in seas and lakes, and that every year some new 

 igneous rocks are produced in the bowels of the earth, but 

 we cannot watch the progress of their formation, and as 

 they are only present to our minds by the aid of reflection, 

 it requires an effort both of the reason and the imagination 

 to appreciate duly their importance. It is, therefore, not 

 surprising that we estimate very imperfectly the result of 

 operations thus unseen by us; and that, when analogous 

 results of former epochs are presented to our inspection, we 

 cannot immediately recognise the analogy. He who has 

 observed the quarrying of stone from a rock, and has seen it 

 shipped for some distant port, and then endeavours to 

 conceive what kind of edifice will be raised by the materials, 

 is in the same predicament as a geologist, who, while he is 

 confined to the land, sees the decomposition of rocks, and 

 the transportation of matter by rivers to the sea, and then 

 endeavours to picture to himself the new strata which 

 Nature is building beneath the waters. 



Prejudices arising from our not seeing subterranean 

 changes. Nor is his position less unfavourable when, be- 

 holding a volcanic eruption, he tries to conceive what changes 

 the column of lava has produced, in its passage upwards, on 

 the intersected strata; or what form the melted matter may 

 assume at great depths on cooling; or what may be the 

 extent of the subterranean rivers and reservoirs of liquid 

 matter far beneath the surface. It should, therefore, be 

 remembered, that the task imposed on those who study the 



* Elements of Geology, 6th edit, 1865; and Student's Elements, 1871. 



