2 Essay introductory to Geology. 



priuciples of deduction ; and although the previous investigation may have 

 occasionally been too hasty, and therefore the conclusion premature, yet 

 this error is incidental to the infancy of every science, and necessarily cor- 

 rects itself as the progress of observation extends. At present, whilst we 

 should modestly acknowledge that much yet remains to be done before the 

 structure of a perfect geological theory can be securely raised, yet we may 

 confidently assert, that very many of the most important elements of such 

 a theory have been ascertained on evidence as incontrovertible asi that 

 which belongs to any other portion of our scientific knowledge. 



To begin with the descriptive portion of Geology, the facts which it 

 brings to our knowledge may be divided into three principal classes. 



I, That the mineral masses constituting the crust of our planet are not, 

 as might at first be ignorantly apprehended, confusedly huddled together 

 in a chaotic mass, but originally disposed with great regularity, in distinct 

 stratiform beds j and although the number of the individual strata be indeed 

 so considerable as to seem to defy the powers of memory, yet we find these 

 strata naturallv associated together in certain definite assemblages, made 

 up of repeated alternations of analogous beds, to which assemblages the term 

 formations has been assigned ; and as the number of these formations is 

 itself limited, the task of committing a clear view of the series of rocks to 

 memory becomes greatly facilitated, and may be still further aided by 

 classing the formations under the more general head of groupes ; and lastly, 

 distributing the groupes under three principal orders — pursuing a system 

 analogous to that by which we arrange the various species of animals — 

 under genera, families, classes, and orders. — Such a tabular arrangement 

 will be shortly submitted to the reader. 



Now as it is ever delightful to discover order where only disorder was 

 suspected to exist, this mental pleasure results in a high degree from this 

 first step in our progress. Nor is it connected with mere intellectual 

 gratification alone, but is moreover immediately subservient to purposes of 

 the very highest statistical and oeconomical importance, for these succes- 

 sive geological formations are very generally each distinguished by the 

 abundance of peculiar metallic minerals, &c. which it contains. Some 

 formations, for instance, being characterised by their ricliness in ores of 

 tin and copper, others by lead and zinc, others again by iron, and by the 

 principal deposits of that most essential element of our commercial pros- 

 perity and domestic comfort, coal. It is the knowledge of the regular 

 order of succession of the mineral formations, as developed by Geology, 

 which alone can direct the practical miner in well-judged and profitable 

 researches for these hidden but important elements of our national 

 wealth, and guard against the disappointment, and often ruinous expense, 

 which so frequently have attended on unsuccessful trials — the issue of 

 which the Geologist would at once have predicted. 



II. Besides these minerals of statistical importance, we find the succes- 



