38 Dr. Mac CuUoch oti the 



the term syenite to compounds occurring both in the family of 

 trap and in granite; and the inconveniences of a similar 

 nature which have been produced, by using the term greenstone 

 in the same vague manner. It is evident, that the same con- 

 fusion, even in a greater degree, would follow from adopting 

 the term basalt in the present case. 



In every instance in which rocks of a similar nature occur in 

 the primary and secondary classes, it is most important to 

 distinguish them by some expedient ; as geological descriptions 

 would either become unintelligible, or be attended with the 

 most inconvenient circumlocution. Limestone has thus been 

 distinguished by the addition of the terms primary and se- 

 condary ; argillaceous schist, by using, in one case, the deno- 

 mination of clay slate, in the other, that of shale. In the cases 

 of granite, and of the trap family, the confusion which would 

 ensue from neglecting to make such a distinction, would be even 

 greater than in the stratified rocks. With an origin far distant 

 in point of time, the members of the trap family are not only 

 found in contact with granite, but they also penetrate it in the 

 form of veins. It is scarcely possible, even with all the as- 

 sistance afforded by a distinct set of terms, to prevent super- 

 ficial geologists, who are contented with the first and obvious 

 appearances before them, from confounding such recent rocks 

 with the more ancient to which they approximate ; and, without 

 such terms, even the most careful observers could not convey 

 accurate information, without danger of misapprehension or 

 without circumlocution. 



As an expedient towards attaining this object in the present 

 instance, it might be suggested that the addition of the adjective 

 terms, primary and secondary, would suffice ; and we should 

 then have primary and secondary basalts and greenstones. 

 But as the term primary has been sometimes applied, by those 

 who only judge from superficial examination, to the recent 

 veins of this nature which penetrate the older rocks, it appears 

 preferable to abandon its use altogether. Perhaps a better 

 expedient will be found by applying the adjective term granitic 

 to the rocks in question. Thus they may be designated by the 



