342 Geology. — On the Order of the Succession of Rocks, 



causes which have deposited all beds. We have said thus much 

 in relation to deficiencies of beds in the general geological series, 

 knowing how necessary it is for students to have proper views of 

 this branch of the subject ; and we take leave of it for the present, 

 with the remark, that our uninitiated readers are to remember 

 that the tabular view we present them with, does not represent 

 any actual section in nature : that we know of no part of the 

 world where all the beds are laid upon each other horizontally 

 in the order here enumerated ; but that some of the beds are 

 found in some countries, and others in other countries, and that 

 in England they have all been found with the exception of the 

 Muschelkalk before mentioned, No. 15; and that wherever each 

 and every bed has been found, it has always been found, as to its 

 place in the series, in the same relative position, never above its 

 superior number, never below its inferior ; from whence we satis- 

 factorily infer, that each of the beds has come in succession into 

 its place ; and that if they were all collected and laid upon each 

 other in one column, the tabular view we have annexed to this 

 article, would be a true representative of it. 



We have now to speak of another class of rocks, which we 

 have excluded altogether from the tabular view, on account of 

 the very irregular manner in which they are found in various 

 parts of the geological series. These have received the generic 

 name of trap, a term derived from the Swedish w^ord trappa, a 

 stair, from rocks of this kind being sometimes found in prismatic 

 forms, rising in stages above each other, and resembling steps or 

 stairs. We refer our readers to our last number, where, at page 

 311, they will find some information about these rocks. Their 

 constituent minerals are generally the same as those which con- 

 stitute modern lavas. The igneous origin of these trap rocks is now 

 universally admitted. Such is the intensity of heat of modern 

 lavas, that they are capable of melting down the older rocks ; and 

 indeed the lava of Skapta Jokul, in Iceland, to which we have 

 referred at page 294, did this to a great extent in 1783, spread- 

 ing itself out into broad lakes of fire, sometimes from twelve to 

 fifteen miles wide, and one hundred feet deep. Eleven years after 

 this period, smoke was still rising from parts of the lava, and hot 

 water was found in several of the fissures. Rocks of this intrusive 

 kind, and of the same mineralogical character, are found in 

 various parts of the geological series, sometimes overlaying in 



