KeilhaiCs Theory of Granite, ^c. 878 



these is, that clay-slate does not contain all the materials of 

 which granite and syenite are formed, and sandstone still less 

 those of porphyry, and the other materials, moreover, are not 

 in such proportions as to enable us, in a chemical point of 

 vie^A', easily to comprehend the possibility of the alleged pro- 

 cesses of change. But this difficulty he has endeavoured to 

 overcome by the before-mentioned proposition, that, if the 

 knowled^'e we derive from chemistry does not suffice, we may 

 be permitted to go beyond it. It has been supposed, that the 

 simple elementary bodies are not so numerous in nature as we 

 are at present obliged to believe ; it may, therefore, be sup- 

 posed, that the small number of actual elements can be changed 

 in different circumstances so as to form different substances, 

 and Keilhau considers it more reasonable to suppose such a con- 

 version than that any new material has been introduced into 

 those regions for the purpose of operating change. Another 

 difficulty connected with the circumstances, is the beds of 

 greenstone in which are found detached pieces of gneiss, 

 and, in general, pieces of the rocks forming the Avails of the 

 veins. These agree with the idea that a melted mass was 

 ejected from beneath, into which pieces of the surrounding 

 rocks had fallen, and been enclosed by the cooling mass. " I 

 willingly admit," says Keilhau, " that the opposing theoretic 

 difficulties are considerable here, but if it should be entirely 

 impossible to overcome them in certain cases, still I find in 

 them no sufficient ground for giving up the views entertained, 

 and returning to those (namely, the Plutonian) which, not 

 merely in one respect, but in many respects, prove to be er- 

 roneous and unreasonable.*"* He contends, moreover, that 

 these opinions are not intended to exclude others, and, if it 

 were possible, that they ought to be placed side by side with 

 the Plutonian theory of formations. Keilhau concludes with 

 a view borrowed from one of the philosophical systems of oiu' 



times.t 



I have now, in as compressed a form as possible, stated 

 Keilhau's theoi-y, and should not have exercised my calling as 

 referee, if Keilhau had not placed so much confidence in my 



* Sec vol. XXV. p. 2G6 and 2C7. 

 t Soc vol. XXV. p. 271 and 2/2. 



