L. A. Necker de Saussure Voyage en Ecosse. 173 



nature, as well as porphyritic slates, porphyries, and aniyg- 

 daloids with a basis of wacke or clay. The above rocks 

 are not found in beds, but in irregular masses, or arranged in 

 prismatic columns, and sometimes in spheres with concentric 

 laminse. These rocks consHtute the principal and character- 

 istic mass of the formation which Werner has named/oeiz trap, 

 a formation which he regards as the most recent of the general 

 and universal deposits. He considers it, with the exception of 

 the alluvial masses, as having once entirely covered all the 

 other rocks; and, but for the numerous revolutions and sub- 

 versions which our globe has experienced, the formation of floetz 

 trap, or of stratiform trap, would still extend, according to this 

 learned geologist, over the whole surface of the earth, and 

 would thus conceal the more ancient formations. 



Mr. Necker considers this hypothesis as inadmissible, be- 

 cause it assigns to the trap formation an extent by far too great. 

 In fact, it occupies at present but a very small surface compa- 

 ratively with the general formations, such as those of the gra- 

 nites, micaceous and argillaceous schists, and especially the 

 sandstones and limestones so abundantly spread over all the 

 parts of the earth with which we are acquainted. The floetz 

 trap formation, on the contrary, dispersed in insulated parcels, 

 and at great distances from one another, occupies merely cer- 

 tain districts, which have no mutual relation. Large countries 

 are entirely without them. They are not found in the great 

 chainsof the Alps, of the Pyrenees, and of the mountains of 

 Sweden and Norway, which comprise, however, a complete 

 succession of the general formations. Other reasons still more 

 powerful oppose the opinion of Werner, relative to his stratiform 

 traps, and authorize us to regard their formation as being of a 

 nature very different from that of the other classes of rocks, 

 and to assign them, in the system of geognosy, a place altoge- 

 ther distinct. 



It has been frequently remarked that from the most ancient 

 primitive deposits whose appearance is entirely granular and 

 crystalline, to the most recent formations which have a dull 

 and earthy aspect, the rocks seem to have diminished in purity, 

 hardness, and tenacity, by a constant gradation. Yet here we 

 have the formation of floiitz trap, which seems to interrupt this 

 uniform march of nature, by presenting to our view the same 

 appearances, the same structure as the primitive rocks, although 

 its origin be comparatively very modern. It has also been often 

 observed, that the more recent the formation of rocks, the 

 greater number tlie variety of animals or plants they contained 

 under the form of petrifactions or impressions. If then, as 

 Werner supposes, the floetz trap be one of the most modern of 

 the great universal deposits formed by precipitation, we ought, 

 by analogy, to suppose it replete with animal or vegetable spoils 



