§21. HYPOGENE ROCKS. 



843 



mineralogy. In these Lectures I must assume that such 

 knowledge is possessed by my readers, or that they will rest 

 satisfied with a general idea of the leading phenomena 

 embraced in this division of the subject* 



Mica-schist and Gneiss. The stratified metamorphic 

 rocks consist of two well-defined groups. The first, or 

 uppermost, is Mica-schist, a slaty rock, abounding in a 

 mineral called mica (from its glittering appearance) ; and 

 quartz, a substance of which rock crystals, and the semi- 

 transparent pebbles common in most beds of shingle or 

 beach, are examples. These two minerals are disposed in 

 alternate layers, forming laminated beds, which are ex- 

 tremely contorted and undulated. The upper divisions of 

 this series bear a considerable resemblance to the metamor- 

 phic argillaceous schists ; the lower are of a more quartzose 

 character, probably from having been subjected to a greater 

 degree of igneous action^ 



Gneiss^ consists of contorted and laminated beds of 

 quartz, felspar, and mica, irregularly stratified ; which may, 

 in truth, be regarded as stratified granite, for the same 

 substances enter into their composition, as prevail in the 

 amorphous masses of that rock. Gneiss is often found 

 associated and alternating with mica-schist, quartz -rock, 

 clay-slate, and a very hard granular rock, called primary 

 limestone. The whole series of stratified metamorphic 

 beds may therefore be considered as partaking of one 



* The elementary mineralogical knowledge necessary for this pur- 

 pose, may be acquired by the study of a suite of specimens to be 

 obtained of Mr. Tennant, 149, Strand, Professor of Mineralogy in 

 King's College. If the student can have the advantage of a few private 

 lessons from Mr. Tennant, or can attend the lectures delivered in 

 King's College, his progress will be more rapid and satisfactory than 

 by any other method. For the advanced student, the " System of 

 Mineralogy," by James D. Dana, second edition, New York, 1844, will 

 be found the best work on the subject, 

 f A German mining term. 



