286 



On the table are specimens of syenites of the diiferent schools, and it will bs 

 at once apparent how much they differ ; it will also be observed how nearly the 

 one approaches a granite, and the other a diorite. 



To compare the definitions of Lyell, Dana, and others :— 



Lyell and Dana. Syenite resembles a granite in which the mica is replaced 

 by hornblende, also that the felspar may be orthoclase or oligoclase ; this 

 is, therefore, eminently acidic, but the acidic character is not constant or 

 characteristic. 



Gotta, on the other hand, says that syenite consists of orthoclase or 

 microlene and hornblende, which may have mica and quartz as accessories, but 

 if either of these are abundant it at once becomes syenitic granite or syenitic 

 gneiss — the difference is more apparent by comparison with diorite and granite. 



SYENITE. 



Dana : — Felspar, quartz, hornblende. 

 Cotta : — Orthoclase, hornblende. 



GRANITE. 



Dana : — Felspar, quartz, mica. 

 Cotta: — Felspar, quartz, mica. 



DIORITE. 



Dana : — ^Felspar and hornblende | 

 Cotta /—Felspar and hornblende j 



From the above it will be at once apparent that the German classification is 



not practical, i. e., it cannot be used in the field, for it is rather too much to 



expect that a geologist, with only an acid bottle, pocket lens, and knife, can 



decide with any degree of certainty on the angles a half-embedded crystal 



makes, or the system it belongs to ; for although orthoclase is monoclinic and 



oligoclase triclinic, still the angles are very nearly the same, (albite) 



118° 120° 86° 90° , , T,, . . ^ XT 1 -n +• 



or or etc., etc. ilie inconverLience ot tnis classification 



a o a o 



is well shown by the fact that Werner, who first proposed it to suit a certain 



rock, subsequently called the same rock a diorite. If, however, the English 



system is adopted, there can be no hesitation in at once determining the quartz, 



felspar, and hornblende ; felspar and hornblende come in as hornblende rock 



if the felspar is decidedly triclinic, if not, as a diorite. 



The English school, or rather the American branch of it, has many claims 



to preference over all others, chiefly on account of its simplicity, and this 



simplicity is insured for some time to come, as the Americans have so^much 



room for real practical science, and cannot afibrd to waste time and talents in 



multiplying names and then finding out some compound to suit them j the old 



proverb about a certain personage finding mischief for idle hands, applies to 



the naturah sciences as well as anything else, for when a certain point has been 



