516 



organic bodies can be carried much further in a short time than 

 had been previously supposed. 



These experiments seem to open a new field of inquiry, and will, 

 I trust, soon be repeated in this country. In endeavouring, how- 

 ever, to verify them, the greatest caution will be required, or we 

 may easily be deceived. We must ascertain, for example, with 

 certainty that every particle of animal or vegetable matter is driven 

 off before we attempt to determine the full extent to which minerali- 

 zation may have proceeded. Professor Goppert is doubtless aware 

 that coniferous wood may be burnt and reduced to charcoal, and 

 after having been kept for some time at a red heat, will continue to 

 exhibit, on being cooled, the discs or reticulated structure to which 

 he alludes. If, therefore, some small particles of carbon remain in the 

 midst of the oxide of iron, such portions may retain traces of the ves- 

 sels peculiar to coniferous wood ; and an observer not on his^guard, 

 might infer that the same structure was preserved throughout the mass. 



In my last address, I alluded to Mr. Lonsdale's detection of vast 

 numbers of microscopic corallines and minute shells in the substance 

 of the white chalk of various counties in England, where this rock 

 had not been suspected of consisting of recognisable organic bodies. 

 I cannot deny myself the pleasure of mentioning the still more sin- 

 gular and unexpected facts brought to light during the last year, by 

 Professor Ehrenberg of Berlin, respecting the origin of tripoli. I 

 need scarcely remind you, that tripoli is a rock of homogeneous 

 appearance, very fragile and usually fissile, almost entirely formed 

 of flint, and which was called polir-schiefer, or polishing slate, by 

 Werner, being used in the arts for polishing stones or metals. 

 There have been many speculations in regard to its origin, but it 

 was a favourite theory of some geologists that it was a siliceous 

 shale hardened by heat. The celebrated tripoli of Bilin in Bohe- 

 mia consists of siliceous grains united together without any visible 

 cement, and is so abundant that one stratum is no less than fourteen 

 feet thick. After a minute examination of this as well as of the tri- 

 poli from Planitz in Saxony, and another variety from Santa Fiora 

 in Tuscany, and one from the Isle of France, Ehrenberg found that 

 the stone is wholly made up of millions of siliceous cases and skele- 

 tons of microscopic animalcules. It is probably known to you, that 

 this distinguished physiologist has devoted many years to the ana- 



