400 Dr. Mac Cull ocH on the Geology of 



cution, and reference to those well-known members which they may 

 chance to resemble. If in these cases we apply the name of any of 

 their species in place of a generic term, we render our description 

 of individuals unintelligible, and often contradictory and absurd. 

 "Thus the name basalt has been given to greenstone, as well as to 

 many other modifications of trap, to which no name has, or perhaps 

 ever can be applied. But the chief confusion has resulted from the 

 application of the term greenstone, as a generic term for these rocks. 

 In this way we have had greenstones of all colours, from red to 

 white, and in which neither hornblende nor felspar were to be dis- 

 tinguished. 



It would assuredly be better in describing the geological appear- 

 ances of these rocks, when the description of individuals is not 

 necessary, to make use of a generic term which should distinguish 

 the character of the family, without confounding the individuals. 

 The peculiar aspect of the rocks of this family renders the name of 

 trap as expressive as any which can be applied, and in this sense, 

 if it be limited to that well-known class of unstratified rocks which 

 includes the above-named individuals and their numerous modifica- 

 tions, we shall escape the confusion which must otherwise ensue, 

 and which unfortunately already exists too much. 



It is evident that the other modifications of this rock consisting 

 of amygdaloid and of the various trap porphyries, are still further 

 subordinate species, if I may style them so, ranking according to 

 their particular basis, under the several species above enumerated. 



It is said that in the Shiant islands ammonites and other animal 

 remains are discovered in beds under the trap, but I did not ob- 

 serve them. They may very probably however exist here, as they 

 are of frequent occurrence in Sky. 



Among the rolled pebbles on the shore I met with specimens of 



