142 TRANSACTIONS OF THE [APR. 21^ 



These cavities, when minute, are filled, and when larger are 

 lined, with beautiful chalcedony, quartz (crystals and pseudo- 

 morphic), prehnite (botryoidal and pseudomorphic), pectolite, 

 datolite, heulandite, etc. 



In some cases the effect is beautiful ; frequently the immedi- 

 ate lining of the cavity (or outer shell of thegeode) is chalcedony, 

 upon which, is the pseudomorphous quartz, which may be coated 

 with quartz or amethyst crystals, and these may be sprinkled 

 with crystals of stilbite or heulandite. Sometimes we find the 

 pseudomorphous quartz covered with yellowish datolite. 



The prehnite, as far as my observation goes, is always found' 

 alone, either in the ordinary botryoidal and reniform shapes, or, 

 when pseudomorphous after pectolite, in the beautiful fan-like 

 radiations which belong to the original mineral. I have observed 

 it in but one part of the quarry, where the rock is more 

 amygdaloidal in its character. 



The great majority of the cavities have evidently been origi- 

 nally lined with pectolite, which has undergone alteration into 

 either silica or prehnite. 



The pectolite is found in every stage of pseudomorphism, 

 from the silky, flexible crystals, in delicate radiating tufts, to- 

 the hard and rigid quartz, chalcedony, or prehnite, taking every 

 imaginable form, from the fan-like radiations several inches 

 across, to masses of quartz composed of what have been prisms 

 of pectolite crossing each other in every conceivable direction. 

 In some cases the pseudomorphism is by incrustation, when we 

 find the masses filled with quadrilateral orifices running in vari- 

 ous directions, looking like blocks into which cut nails have 

 been driven and extracted, — in other words, like nail-holes. 



Some of the solid masses, when the change is chalcedonic, 

 make beautiful agates when polished. We also find agate in its 

 natural concentric forms. 



Some of the cavities are lined with quartz crystals with no 

 evidence of pseudomorphism ; but in most cases these quartz 

 crystals are backed by a layer of massive quartz or chalcedony 

 with pseudomorphous markings. Many of these crystals are 

 amethystine in color; one amethyst geode I have, with crystals 

 containing phantoms. 



In many cases the crystals are thickly sprinkled with micro- 

 scopic crystals of what I think is cuprite, embedded in the 

 surface of the crystals, and sometimes even in their interior, 

 forming beautiful inclusions. 



In most cases the quartz pseudomorphs are milky-white, but 

 some of the specimens I have are stained red, probably with 

 cuprite ; and one specimen is stained a bright malachite green. 



Most of the red crystals are exceedingly fine radiations spread 



