106 Association of American Geologists and Naturalists. 



report of further determinations, by the same process of research, 

 was promised for a future meeting. 



P?'o/. R. E. Rogers described a new apparatus and processes, 

 devised by himself and Prof. W. B. Rogers, for the determina- 

 tion of the amount of iron in iron ores, cast iron, &c. They are 

 a platinum bulb and stem in place of the usual implement of 

 glass, and, by a peculiar construction, ^.revolving motion is given 

 to it, while hydrogen is passed over the heated assay. As a great 

 improvement in the process of reduction, the Profs. Rogers have 

 recently, with great success, employed lampblack in mixture 

 with the ore in a platina crucible, the reduction being effected in 

 a few minutes by a spirit lamp and current of air. The amount 

 of metal is determined by the volume of hydrogen disengaged by 

 the action of dilute acid in a graduated syphon tube. 



Prof. John Locke made some oral observations on the lead re- 

 gions of the Upper Mississippi. Mr. Conrad had announced that 

 these deposits were equivalent to the Trenton limestone, as in- 

 dicated by the fossils, some of them having lead replacing the 

 animal form. Dr. L. remarked that that portion of the formation 

 furnishing the fossils of Mr. Conrad was not productive in ga- 

 lena. Mr. Owen and himself had determined the principal de- 

 posits of lead to be found in a peculiar rock equivalent to the 

 cliff limestone. He had no doubt of the accuracy of Mr. Con- 

 rad's conclusions, as far as he (Mr. C.) had had an opportunity of 

 determining the equivalency from the specimens submitted to 

 him. 



Doctor Houghton added his assent on the determination, but 

 did not think any peculiar limestone essential to the occurrence of 

 lead. He had formed the opinion that it had, in all cases Avhich 

 had come under his observation, been segregated and sublimed 

 by the heat of intrusive trap. In Michigan he had uniformly 

 found native copper near and attached to the numerous trap 

 dykes, while sulphuret of lead was lodged in cavities of the 

 rocks more remote from the heat. 



Prof R. E. Rogers said that the fact corresponded to what 

 might be expected where sulphurets of copper and lead were 

 heated together ; the former would be reduced to metallic copper 

 by the heat alone, while the galena would be driven into the 

 cooler parts of the rock. 



