of the Chalk Formation. 259 



already been shewn to agree with the large, with regard to 

 the effect of external influences upon them. 



7. The period of the dawn of the organic creation co-ex- 

 istent Avith ourselves, can only be admitted as being anterior 

 to, and below, the chalk formation, if indeed, which is ques- 

 tionable, such a distinction can be made ; or the chalk, with 

 its rocks, covering far and high the superficies of the earth, 

 forms part of the series of recent formations, and some of the 

 four as yet well established great geological periods of the 

 earth's formation, the quaternary, tertiary, and secondary for- 

 mations, contain recent organisms, it is, as three to one, more 

 probable that the transition or primary formation is not dif- 

 ferently circumstanced ; but that, from the gradual longer 

 chemical decomposition and change of many of its organic 

 relations, it is more difficult to examine and determine. 



Paludina vivipara and C'^clas cornea of the Weald clay, 

 and the recent Trochus below the chalk, according to De- 

 france, as well as the confirmation of the occurrence of Tere- 

 bratula caput Serpentis in the upper Jura formation, by Von 

 Buch, together with my observations of microscopic, yet, 

 nevertheless, peculiar Polythalamia in the flints of the Jura, 

 are additional positive indications of the inconceivable ex- 

 tent of similar organic relations, the further investigation of 

 which is one of the important questions to be determined in 

 the present age. 



8. It cannot be denied that the notion hitherto frequently 

 asserted, that all recent organisms, including man, are the 

 descendants and perfected stages of metamorphoses of trilo- 

 bites and ferns, has something in it opposed to sound sense ; 

 when, therefore, the direct inquiry leads powerfully to a dif- 

 ferent point of view, it has much in its favour, even though it 

 be reserved to a future period, to explain the vast connection 

 of the phenomena. 



9. Since now, Polythalamia, and other forms identical with 

 chalk animals, exist, which are not endowed with spontaneous 

 division, this faculty of the Infusoria, and their general nature, 

 are not the sole causes to which the indefinite duration of the 

 species is owing. 



