94 GRANITE. 



the laminar disposition sufficiently common in this 

 rock. This presents a considerable analogy to the 

 similar forms in the porphyries ; the laminae being ex- 

 ceedingly variable in extent, but rarely very continuous 

 without interruption, as strata are, but commonly of dif- 

 ferent thickness in different parts; or irregularly ex- 

 tenuated and encreased. Nor are they prolonged ac- 

 cording to the dips or bearings of the surrounding 

 strata, which, under certain variations, always preserve 

 some general tendency. On the contrary, they are al- 

 ways irregularly placed, even when in immediate contact 

 with these, so as to occupy every possible position 

 within a very limited space. In such beds the straight 

 passes into the curved form, or, finally, into a large 

 spheroidal structure. The prismatic form is some- 

 times also combined with the laminar, as in the por- 

 phyries ; to which, in all else, granite presents a strong 

 analogy. The thickness of the laminae is various ; 

 sometimes descending to a structure which has been 

 improperly called schistose. Hypersthene rock, which 

 is an unstratified Trap, presents equally all these fea- 

 tures ; and hence, in each case, they must be consi- 

 dered as modifications of a concretionary structure. 

 The magnitude of the objects is a 'circumstance of no 

 account in the extended operations of Nature : nor 

 need I do more than remind the reader of the pinna- 

 cles of the Alps, where observers, who should have 

 known better, have imagined an erected stratification. 

 Granite beds sometimes present other forms, by 

 which this rock is recognized, even at a distance ; 

 though they occur also in the older sandstone. These, 

 the short prismatic and cuboidal, are, however, partly 

 the result of an incipient decomposition. The beds 

 are originally intersected by fissures, often at right an- 

 gles, which under exposure to air and water, enlarge, 



