194 THE WONDERS OF GEOLOGY. Lect. 111. 



and our views enlarged, the harmony and unity of nature 

 become more and more manifest ; the apparent breaks in the 

 chain of causation exist only in our imperfect conceptions. 

 These considerations will not, however, affect those leading 

 principles of Geology which it is my present endeavour to 

 render familiar to the intelligent but unscientific inquirer. 



In pursuance of this object we will first take a general 

 view of the nature of the mineral substances which enter 

 into the composition of the crust of the earth, and briefly 

 notice the laws which regulate the deposition of sedimen- 

 tary detritus in the beds of rivers, and in the depths of the 

 ocean. 



2. Mineral composition of rocks. — Every substance 

 is composed of atoms of inconceivable minuteness, held 

 together by a principle termed attraction or cohesion, and 

 which is probably a modification of that influence, which, 

 as it exists under certain conditions in inorganic substances, 

 is called electricity, galvanism, or magnetism ; and in 

 organized beings, nervous influence.* The different states 

 of solidity, fluidity, and vapour, in which every material 

 body may exist, were exemplified in a former lecture, and 

 we need only remark, that of the substances, which in the 

 present state of chemical knowledge are considered simple 

 or elementary, about sixteen constitute, in their various 

 combinations, by far the largest amount of all organic 

 and inorganic matter. Of these, eight are non-metallic ; 

 viz. oxygen, hydrogen, nitrogen, carbon, sulphur, c.hlorine, 

 fluorine, and j^osphorus ; the four first are almost always 

 found in combination. Oxygen constitutes one-fifth part 

 of the atmosphere, and eight-ninths in weight of water, 

 and a large proportion of every kind of rock. Hydrogen 

 makes up the remaining portion of w T ater ; and Nitrogen 



* See a masterly " Essay on the Correlation of Physical Forces," by 

 W. B. Grove, Esq. F.R.S. London, 1846. 



