274 



about 74° and 106°, or nearly those of calc-spar or carbonate of 

 iron. Could either of these have formed the cavity ? It is evi- 

 dent from the internal form of it that they could not ; and if any 

 substance ever occupied the space, it got there by infiltration, and 

 took its form from the cavity, without communicating any to it — 

 thus producing a kind of pseudo-morphous crystal. The cavity 

 enlarges, towards the surface of the crystal, by successive step- 

 like ridges parallel and continuous nearly all around it. These 

 ridges are also parallel with the face of the crystal, and ihey 

 indicate an interruption in the process of crystallization by some 

 cause not easily explained. The sides of the cavity do not con- 

 form to any of the striae of the crystal, but they are nearly par- 

 allel with the small rhombic replacements resting on the adja- 

 cent lateral angles of the prism which are occasionally seen on 

 quartz crystals from other localities, rhombifere of Haiiy. The 

 annexed cut represents the appearance of the cavity, drawn in 

 full size from a cast of it. The position is reversed, the face 

 lettered F being the bottom of the cavity in the crystal, and cor- 

 responding with face F of the crystal. Mr. Alger wished to call 

 the attention of other mineralogists to the subject, and desired 

 them to search for other specimens that might throw more light 

 upon it.* 



Dr. Cabot announced the donation from Mr. Theodore 

 Lyman of %20 for the department of Ornithology. The 

 thanks of the Society were voted for the donation. 



A Geological Map of England was presented by Mr. Bul- 

 finch. 



Dr. Burnett presented a specimen of Prairie Grass of 

 unknown species, seven and a half feet high. 



* A cellular quartz has been found in the vicinity of Lancaster, Penn. and de- 

 scribed by Dr. Atlee in the American Journal of Science, Vol. XXXV. p. 139. 

 But here the cavities presented no anomalous character, but were obviously pro- 

 duced by calcareous spar, precisely like those from Herkimer County, New York. 



