to those with which they are connected, since they interfere not only with the primary ones, but with almost the latest of the secondary, and are frequently found lying indifferently both above and below these latter. Hence have arisen distinctions which are often merely nominal, and founded on false theoretic views, of traps of one or other age, of first, second, third, and newest formations. The same identical mass will often possess the characters of all these, since it will in one place be found incumbent on the latest, in another on the most ancient rocks. Except this, I know not that any certain marks of distinction can be pointed out among the several traps. In the greater number of instances at least which have fallen under my examination, such a relation between an unstratified rock, occupying the irregular and uncertain position which trap does, and those regularly stratified ones which maintain a constant order of succession, is by no means a criterion by which to judge of its relative order with regard to these. The aid of a diagram is perhaps required to render this statement intelligible to those who have not examined the rocks for themselves.[1] The same mass of trap will be found in one place incumbent on clay slate, in another on red sandstone, in a third on shelly limestone, in a fourth on the uppermost secondary strata. In such a case when the separate portions are either not all accessible, or when they lie far distant and interruptedly, we might be easily led to conclude that they were so many distinct deposits, and thus apply to them terms derived from the particular beds with which they were found immediately in contact. A more intimate acquaintance with them, and with the general nature of trap is required to correct these erroneous conclusions, and the accompanying[1] sketch, will explain that which actually occurs in nature, and of which, if I mistake not, instances are
Page:Transactions of the Geological Society, 1st series, vol. 3.djvu/60
