. Detrital Theory of Geology. 299 



But whilst the distinction of epochs or eras is rejected as 

 being totally inapplicable to any particular formation, as 

 regards the period of deposition in all parts of the earth at one 

 and the same time, yet, on the other hand, it is maintained 

 that, in any given area or locality on the earth's surface, 

 every stratum there found super-imposed upon another, is 

 as distinct and separate in relation to time as the several 

 strata therein contained are distinct from each other. 



Hence any given locality, from the strata it contains, 

 correctly expresses according to the detrital theory, by the 

 order of super-position, the relative periods or epochs at 

 which each individual stratum therein contained was 

 formed ; and, also, from the depth and contents of each 

 stratum, the length of period required for its formation is 

 surmised. 



It is the purport of this paper to question the validity of 

 DETRITUS, as being a sufficient means of explaining the 

 formation of strata, and, therefore, of the value of Strati- 

 fication as a means of determining the age of the earth, or 

 how far we are justified in viewing it as a chronological 

 chart. 



The original crust of the earth, whether regarded as of 

 aqueous or igneous origin, is admitted on all hands to have 

 been GRANITE, and is thus described by a well-known 

 author: "The unstratified or igneous rocks occur in no 

 regular succession, but appear amidst the stratified without 

 order or arrangement, heaving them out of their original 

 horizontal positions, breaking through them in volcanic 

 masses, and sometimes over-running them after the manner 

 of liquid lava. From these circumstances they are in 

 general better known by their mineral composition than by 

 their order of occurrence. Still it may be convenient to 

 divide them into three great classes granitic, trappean, and 

 volcanic ; granitic being the basis of all known rocks, and 



