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respecting the silicification and consequent preservation of organ- 

 isms, — that the process proceeded, step by step, with the change 

 of the organism into gaseous or aqueous matter. The mollusca 

 may be considered as simply organized water, for one hundred 

 parts by weight, often contain ninety-seven parts of water, vola- 

 tile at 150° F. The cell walls of albumino-gelatinous matter are 

 permeable, and the infiltration of aqueous solutions of silicate 

 of lime, would displace the water, gradually depositing silica in 

 a hydrous state, while the lime passed out with the water. As 

 consolidation is hastened by the decomposition of the animal 

 matter, the cell walls become changed, and the carbon or humus, 

 in excess over that which can become gaseous or aqueous, 

 remains ; retaining as a mere skeleton the forms of the walls. 

 These silicified forms are always porous, and the flints contain 

 the carbon of the organic matter, unevenly distributed. As a 

 beautiful illustration of silicification, he referred to the specimens 

 of trees from California, frequently found in the explorations 

 for gold ; many of the specimens presenting the sap vessels 

 entire in all their delicate organization and nearly natural color, 

 while near by, on the same piece, may be seen black portions, 

 in which the organized forms are lost, and the color is deep black. 

 This striking diversity is due to the fact that the wood at some 

 points had passed into the last stage of humus, — carbon and 

 water, — before silicification took place, and hence the specimens 

 present us with both silicified wood and silicified charcoal. He 

 observed the same changes, though less obvious, while examining 

 the highly interesting locality on the Island of Antigua, and at a ' 

 future meeting will exhibit illustrative specimens. 



Dr. C. T. Jackson remarked that he had examined the mate- 

 rials which enter into the composition and cementation of sand- 

 stones and conglomerates, and had found the cements to be differ- 

 ent in different cases. In some, carbonate of lime forms the 

 principal cement, in others, oxide of iron composed a large propor- 

 tion of the cementing matters, and in others, finer particles of 

 the same I'ocks that composed the conglomerate had formed a 

 paste, which had been hardened by the agency of heat and by 

 the production of silicate of lime derived, undoubtedly, from the 

 decomposition of chloride of calcium. He stated that when peb- 



