150 QUARTERLY JOURNAL. 



Prof Rogers said it was hicrhly important that the angles of the 

 rhombs, &c., mentioned by Dr. Barrett, should be measured. He 

 conceived that the temperature of the earth, at the time of the 

 formation of the sandstone, was far above any possible point ol 

 the crystalization of water. n i . . 



Dr. Barrett said that he did not refer to structure at all, but tc 

 indentations in the mud. 



Prof. Rogers said that, still, there was a kind of indentatior 

 that belonged to structure. , , . , i i .1 



Dr Barrett said he was satisfied that, by the features he had tha- 

 day explained, he could readily determine the temperature of th.i 

 earth at that " very olden time," within about twenty degrees. 



Prof SiUiman said that, if they went on with this subject, the^.- 

 would freeze up all their time. He moved to drop the subject fo 

 the present time. 



A very interesting and curious paper was tlien read by Mr 



Dana, on the minerals of the trap rock series. j 



Dr. Jackson followed with very able and unusually clear ra 



marks, on the subject of the minerals of trap dykes. He said tha 



wherever two rocks come together, one of igneous and the othe 



of aqueous origin, there is always a chemical action between them 



Not so, or scarcely to any extent, where a rock of igneous origi', 



goes through a rock like limestone, which though of aqueous on 



ein, has undergone chemical action and crystalized. For exampU 



when trap dyke goes through lime rocks, the rocks unite withoij 



any commotion, and a pure silicate of lime is formed, bo \vb^ 



the trap passes through clay rocks or clay slate, the slate is bakj 



hard, and jasper and jasper minerals are formed. So when M 



trap passes through granite, no amygdyloid is formed But wh( 



the trap passes through sandstone rock, you then see that there h: 



been a violent tumult— considerable effervescence, and eitlr 



amyf^dyloid is formed, or a trap tufa which is sometimes poro' 



and cellular, as the scoria or lava of the volcanic regions of L+i" 



&c Again, where the trap rock runs through granite, we 



sulphurets of iron formed ; where the trap goes through clay slat 



we find the same minerals resulting : when the trap goes throm 



limestone, we find galena and the ores of zinc ; and where the tn 



p-oes through the red sandstone, we find copper produced, ihisi 



peculiarly the case in Nova Scotia ; no lead is found in the tn 



there, but pure copper ; the sulphurets of copper lay in the san. 



stone : heat was required to expel the sulphur ; nature did t^ 



when forcing the heated trap rocks through the sandstone, and tJ 



pure copper is thus reduced from the ore. We see abundant e^ 



dence of this also, in the copper of Lake Superior, where the saD 



process has been going on. [Specimens were here shown 



Abundance of sulphurets of copper are found in the red sandston 



filling fossil plants. 



