Geological Poems. 285 



To make Amygdaloid. 



Take a mountain of Wacke^, somewhat softish and green, 

 ]n which bladder-shaped holes may be every where seen ; 

 Choose a part where these holes are decidedly void all, 

 Pour^ilex in these, to form Agates spheroidal, 

 And the mass in a trice will be Amygdaloidal. 



To make a good Breccia with a Calcai-eous Cement. 



Break your rocks in sharp fragments, preserving the angles ; 

 Of Mica or Quartz you may add a few spangles : 

 Then let your white batter be well filtered through, 

 Till the parts stick as firm as if fastened by glue. 



To mahe a coarser Breccia. 



For a Breccia more coarse you may vary your matter ; 

 Pound Clay, Quartz, and Iron-stone, moisten'd with water ; 

 Pour these on your fragments, and then "wait awhile, 

 Till the Oxyd of Iron is red as a tile^. 



2 Wacke. See Primer, p. 24. Wacke is generally greenish, and rather 

 unctuous to the touch. This rock must not be confounded with Grey- 

 Wacc6. 



3 The geological Neophyte who attempts to make aggregated rocks from 

 the above approved receipts, should attend to the following directions : — 

 Granite rocks must be composed of crystalline grains of two or more differ- 

 ent species of minerals closely united without any cement— Porphyry, of a 

 base or paste containing imbedded crystals (generally of felspar)— Pudding- 

 stone, of rounded stones plentifully imbedded in a siliceous paste — Amygda- 

 loid, of basalt or wacke inclosing nodules of agate or chalcedony — Breccia, 

 of angular fragments of any kind of rock, united by a cement. When large 

 rounded pieces mixed with fragments are held together by a cement, it is 

 generally called a coarse conglomerate. 



Vol. V....NO. If. 37 



