140 JOURNAL OF THE [July, 



describe or draw it at any moment. But we do not know what 

 to expect when we come to examine a thin section of granite. 

 We may have seen hundreds of sections of granite before, yet, 

 even if we had seen thousands and tens of thousands, this would 

 not warrant us to draw any conclusions as to the appearance of 

 the specimen in question. For the chances are a thousand to 

 one against our having ever seen anything like it. 



There are no two granites alike, just as there are no two lavas, 

 basalts, or other igneous rocks alike. The differences in their 

 microscopical structure are perfectly astonishing, especially in 

 specimens of the same kind of rock from different localities. 

 But even different pieces of granite from the same locality may 

 present an almost infinite variety of structural detail. And of 

 twenty sections from one small piece, not larger than a walnut, 

 not two will be found alike. The only kinds of rocks which 

 exhibit a close resemblance, even if taken from different localities, 

 are certain fine-grained sandstones, slates and other sedimentary 

 formations; and even these, if carefully examined, will be found 

 to show marked differences. 



The conclusions, which such variations and differences enable 

 us to draw, do not affect the life-history of some obscure insect, 

 or the derivation of a fungus, but involve cosmic problems of 

 universal importance ; the history of the crust of our planet, 

 cycles of marvellous changes in the abysmal ages of the past, 

 the disintegration and re-formation of the earth's material, and 

 the life of those extraordinary and mysterious bodies, the 

 crystals. 



The time is fast approaching, when the microscope will be as 

 indispensable to the progressive geologist, as it has been already, 

 for a considerable number of years, to the zoologist, the botanist 

 and the physician. Indeed, even at the present moment, the 

 foremost inquirers in some of the most important departments 

 of geological science depend so much on the aid of the micro- 

 scope in their researches, that they would be almost helpless 

 without it. If that instrument has vastly added to our knowledge 

 of vegetable or animal structure, if it has enlarged our horizon 

 to an immeasurable extent in the domains of the organic world, 

 it is accomplishing at present equally important results in the 

 domain of inorganic nature, for it has completely revolutionized 

 the study of rocks. Some of the facts which have already been 



