•404 Met amoral asm. 



crevices and fissures more or less filled up with foreign ingre- 

 dients that characterize certain districts, lie will find still more 

 striking examples of change in the arrangement of the atoms 

 of various substances quite independent of any change of 

 external form. He will find calcareous shells becoming siliceous, 

 still retaining their minute structure ; trunks of trees also 

 silicified, from which he can get slices for the microscope that 

 will exhibit all the details of organization ; hollow flints and 

 other stones, with a perfect lining of the most beautiful 

 crystals. 



If he visit Wales and Cornwall, and can examine slate 

 quarries and places where such rock as granite is worked, he 

 will find structure so new and peculiar, so complicated and so 

 curious, that he will fancy himself studying the remains of 

 another world; he will then begin to think of molten rock 

 penetrating into and altering the other rocks ; he will dream 

 of the deep recesses of the earth where abundant stores of 

 fluid granite are always ready at hand to perform nature's 

 miracles ; where all the marvellous phenomena of volcanoes are 

 prepared, and where, in fact, having reached Vulcan's workshop 

 and nature's laboratory, he is at liberty to amuse himself with 

 all the explosive compounds, the great furnaces, the powerful 

 acids, and the overwhelming forces he believes to exist there, 

 and thus settle all the difficulties of geology at one effort. It 

 would be strange if with all these facilities of producing dis- 

 turbance, our adventurous, but still dreaming student, did not 

 give way to temptation and return from dreamland a confirmed 

 A'ulcanist, referring every disputed point to some result of the 

 action of fire on the materials beneath his feet, knowing nothing- 

 whatever meanwhile of the condition of the earth's interior, of 

 the mode in which rocks are changed, or of the connection 

 between volcanic phenomena, which are really igneous, and 

 those that have produced granite and modified clays and lime- 

 stones at great and unknown depths beneath the earth's surface. 



The earlier geologists were, in fact, in the position here 

 indicated, and have behaved in a manner not very different 

 from that of our dreaming student, and their dreams have 

 unfortunately been accepted as sound conclusions, occupying a 

 prominent place in most popular works on geology of the pre- 

 sent day. There has been a long and hard struggle for many 

 years to found another school of geology^ to question nature a 

 little more closely as to her style of work in reference to these 

 altered rocks, without these gratuitous assumptions, and to put 

 aside as a matter to be inquired about and not taken for granted, 

 the influence of intense melting: heat in the interior of the 

 earth, within those narrow limits that come within human obser- 

 vation, and which alone have been concerned in the work of 

 metamorphosis. 



