The position, extent, and direction of the several strata of different formations, either taken with or without reference to the fundamental rock, yield very con vincing testimony in favour of the opi nions delivered by the celebrated Werner respecting the formation of the earth. (See GEOLOGY.) Previously to viewing the illustration of his theory in the forma tion of a suite of rocks, it may be neces sary to particularize some of the pecu liarities in the formation of different rocks, and to show the different terms by which they are expressed. The for mations themselves are distinguished as universal or partial, and as unbroken or broken. The strata are considered as conformable, or unconformable, with the direction of the fundamental rock ; and overlying, when lying over the ends of the strata of the fundamental rock. They are said to be straight, when disposed in one direction on the fundamental rock ; when they turn round it, leaving the top uncovered, mantle-formed ; and when they also cover its extremities, saddle thinned. When concave, they are termed basin-shaped ; and if the concavity is long, trough-shaped. Their upper extre mities, appearing at the surface of the earth, are termed the outgoings of the strati : the outermost of the circles form ed by these is the oldest in the concave (the basin and trough-shaped), and new est in the convex (the mantle and saddle shaped). When detached portions occur on the summits of hills, they are called caps ; when filling up hollow spaces, up fillings ; and when only on one side of a mountain, shield•formed.
It has been here said, according to the theory of 'Werner, that one class of mountains was deposited, by chemical formation, from an aqueous solution, pre vious to the creation of vegetables and animals : that to these succeeded another class, in which materials mechanically se parated were discoverable, formed dur ing the passage of this globe into a habit able state ; and that during the existence of animals and vegetables in considerable number, another (the latest) class was produced, in which mechanical deposits and remains of organized bodies exist in considerable quantity. Of these different
classes of rocks, it may be expected, that the rocks of the earliest period would be found invested in various modes by those of later formation, and disposed in the or der of their separation from the waters from which they derived their origin.
The rocks which exist in the Hartz ap pear to be beautifully illustrative of this successive deposition. In the centre a vast mass of granite rises through the other strata, and round this clay-slate is disposed in mantle-shaped strata. Gneiss and mica-slate not existing in this coun try, transition limestone succeeds to the clay-slate, and then grey wack6 and grey wacke slate : the whole being wrapped round the granite in mantle-shaped stra ta, and invariably with lower and lower outgoings, corresponding to the newer and newer strata. To these the floetz rocks succeed, the oldest of the floetz resting on the newest of the transition ; and the different floetz rocks resting on each other according to their relative age. Last of all, the alluvial rocks are found in the lowest situations. We have thus, as Mr.. Jameson observes, all the series of rocks, from the granite to the alluvial, marked with a diminishing le vel, in proportion to the newness of the strata.
The system of Werner, formed upon a most comprehensive view of the several phenomena observable in the formation of the crust of this globe, has been here adopted, from Professor Jameson's per spicuous description of it, on account of its so exactly corresponding with the ap pearances which masses of rocks every where present to our view. The present outline, though perhaps sufficiently cor rect, is, however, by no means pretend ed to supersede the study of the work alluded to ; since an accurate knowledge of the subject can only be yielded by the study of the more highly finished per formance itself.