142 JOURNAL OF THE [july, 



mineral could be distinguished by the form, color, etc., of its 

 crystals, and it was found that even the most fine grained rock 

 was not, as formerly believed, a mixture of shapeless ingredients, 

 but consisted of minute crystals, sometimes of the most 

 exquisite outlines. 



Especially striking and lovely is the appearance of many of 

 the volcanic or igneous rocks, when reduced to thin sections, 

 and examined under the microscope. The dullish green lava, 

 called pitch-stone, which is found in dykes on the isle of Arran, 

 on the west coast of Scotland, exhibits under the microscope 

 whole forests of fern-trees, garlands, leaves and flowers of mar- 

 vellous magnificence. A certain granite from Cornwall contains 

 needle-shaped crystals of tourmaline, radiating star-like from a 

 common centre. Basalts, obsidians, porphyries, serpentines from 

 various localities show labyrinths of multicolored crystals, re- 

 sembling rows of pillars, turreted castles and fairy caves, glow- 

 ing in all tints of the rain-bow. 



The sedimentary or stratified rocks, while they cannot equal 

 under the microscope their plutonic rivals, in brilliancy of color 

 or gorgeousness of crystalline display, make up this deficiency 

 by other features of interest, compensating the inquirer by 

 revelations of a different character, but none the less re- 

 markable. 



Many marbles and limestones are found to be literally com- 

 posed of foraminifera, the tests of rhizopods, resembling tiny 

 shells of the most delicate and beautiful forms, which were de- 

 posited on the ancient sea-bottoms, accumulating in the course 

 of ages to a height of hundreds, nay, thousands of feet, every 

 inch of which represents at least several centuries. Thin sec- 

 tions of almost any piece of flint exhibit under the microscope 

 quite a little world of curious organic remains, such as sponge 

 spicules, xanthidia, small fragments of coral, and the foraminifera 

 already mentioned, furnishing very strong evidence that the 

 flints are silicified fossil sponges. 



It would be in vain for me to attempt here anything like a 

 detailed description of the discoveries, which have resulted from 

 the microscopical examination of rocks. This branch of study, 

 though barely thirty years old, has already contributed such a 

 vast deal of new information to natural science, that it has, in 



