504 



THE GEOLOGIST. 



and interesting sponges, and through the kindness of the author I am 

 able to give outline drawings of the most characteristic forms. One 

 of the principal objects he had in view was to show that the different 

 species described by Goldfuss and Homer are only varieties. 



Professor Kjerulf, of Christiania, read a paper on the extension and 

 origin of the iron ores of Norway, which he argued are due to erup- 

 tion ; and, as far as the manner of their occurrence is concerned, 

 may be well compared with trap dikes. At the same time, by the 

 term eruptive he did not necessarily mean that they were of mere 

 igneous origin. 



Dr. Blialoblotsky brought forward various objections to the theory 

 of the purely igneous origin of granite. As is well known, and as 

 has been pointed out by many authors, those difficulties are so great, 

 that not a few geologists have gone into the opposite extreme, and 

 almost entirely denied the instrumentality of an elevated temperature. 

 Since I myself have argued against both these extreme views, and in 

 favour of a theory which I look upon as a sort of happy medium, I 

 am so far prejudiced as to admit the truth of some of the author's ob- 

 jections, but to think he carried his conclusions too far against the 

 igneous theory. 



Dr. Volger afterwards exhibited and described some pebbles, said 

 to be sometimes water-worn, which occur in a brecciated vein. The 

 spaces between the fragments and pebbles are filled with a crystalline 

 deposit of quartz and felspar, and thus the deposition of those mine- 

 rals from water (most likely at a high temperature) is rendered very 

 probable. 



Professor Blum read a paper on some peculiar agates. In one 

 case there had been a horizontal deposit at the bottom of the cavity, 

 and then the upper part had been at first coated over with a con- 

 centric layer of chalcedony, and finally filled with crystalline quartz. 

 The chalcedony having been subsequently removed, the nucleus of 

 quartz was left quite loose and unattached in the upper part of the 

 cavity. This communication gave rise to a lengthened discussion, in 

 which Dr. Yolger said that in his opinion agates were not usually 

 formed by the direct introduction of siliceous matter into empty cavi- 

 ties, but that there previously existed either a piece of limestone or a 

 cavity that had been filled with calcareous spar, which had subse- 

 quently been replaced by agate. In this manner he would explain why 

 in many cases the layers of agate are of such an uniform thickness both 

 at the top and bottom, which he contends would not have been the 

 case if they had been empty cavities filled directly. In support of 

 his views he described some interesting veins in Saxony, which at a 

 great depth are calc-spar, higher up a mixture of this with chalce- 

 dony, and at the top only the latter with pseudomorphs in the form 

 of calcite, thus proving its replacement by chalcedony. After this. 

 Professor Schonbein exhibited some fluor-spar, which when pulve 

 rized gave off ozone. Hitherto he had met with such specimens a- 

 only two localities, but suggested that mineralogists should examin 



