249 



of Iron. It contains Silica, about fifty per cent. ; Protoxide of 

 Iron, twenty ; Alumina, seven ; Potash, ten ; Lime and wa- 

 ter. From its physical characters, Prof. Rogers was inclined 

 to regard it as an original deposit. Had it been of mechanical 

 origin it would have contained conglomerates and been mixed 

 with other minerals, which is not the case. Neither is there any 

 green rock known from which it could have been derived. His 

 theory was, that at the time when the southern part of the 

 United States was submerged, the green sand was deposited from 

 the Gulf Stream. The water he supposed to have been charged 

 with soluble silicates of volcanic origin somewhere at the south, 

 perhaps in the region of the West Indies, which were precipi- 

 tated as the current reached the cooler latitudes of the north. 



Dr. C. T. Jackson said, he agreed with Prof. Rogers in his expla- 

 nation of the green sand deposit. The process would be similar 

 to that of the drying of French green. He suggested thermal 

 springs as another source from which such a deposit might be 

 derived. 



Dr. Burnett announced, that he had recently found parasites in 

 the human ovum. They belonged to a species of Conferva sim- 

 ilar to the yeast plant. They appeared in triplets, or by twos, 

 and were about ^^Vo- of an inch in diameter. It was difficult to 

 account for the presence of these parasites in such a situation, as 

 their spores would be too large to be deposited from the circula- 

 tion by passing through the v^^alls of the blood vessels. 



Mr. Desor described the origin of the Madreporic body in 

 Starfishes. It had recently been explained by John Muller, of 

 Berlin, as the scar of the attachment of the Starfish to a Medusa- 

 like body by which it is surrounded, and to which it is attached 

 in the embryonic state. Mr. Desor explained this condition by 

 diagrams on the blackboard. He stated the curious fact that he 

 had noticed in the Syncoryne, a similar scar. It was due, he 

 said, to the same cause, the attachment of the embryonic jelly- 

 fish to the parent polyp. 



Mr. Alger exhibited some magnified drawings of vermiform 

 mica, from Waterbury, Vt. The mica was found on the surface 

 and in the substance of quartz crystals, and when examined 

 under the microscope was found to present very singular and 



