376 Mr. Weaver's View o/'Ehrenberg's Observations 



is throiigliout more perfect than it is in many flints, although 

 the constituent elements of both kinds of stone are very pro- 

 bably cjuite the same. 



On the jvincipal Organic Calcareous Forms 'which C07nj)0se 

 the mass of all Chalk. 



From what has been already stated, it is evident that the 

 production of the calcareous mass of the chalk is not to be 

 attributed, as formerly conceived, to the larger organic bodies, 

 but to the minuter, and in the greatest measure to such as 

 are invisible, consisting of eight genera of Polythalamia with 

 twenty-five species, and excluding all such as may be distin- 

 guished by the naked eye, that is, exceeding tj't^^^ ^^ ^ ^'"^ ''• 

 magnitude; the latter, however, are comparatively rare. It 

 is possible that several other, and perhaps many species of the 

 same genera, may yet be discovered in the chalk, as well as 

 other genera, since the investigations hitherto made could 

 only be applietl to a minimum of its substance; yet, as these 

 were conducted by me on chalk from many regions, it does 

 not appear jMobable that other sections of the animal king- 

 dom will be found to have taken so great a share in the foini- 

 ation of chalk as the Polythalamia, the principal prevailing 

 forms of which I have indicated. 



From the preceding it is also apparent that the chalk rocks 

 of all countries agree in their constituent organic forms not 

 only according to the zoological class, but also in genera, and 

 for the most part in species likewise; this character being not 

 confined to the white tender writing chalk of Europe, but ex- 

 tending also to the compact limestone rocks of the North of 

 Africa and the West of Asia. Particularly striking is the 

 characteristic persistence of single forms through all these 

 different and widely-separated countries. Thus in all of them 

 are to be found Rotalia globulosa, with lexlularia globnlosa^ 

 7". aciculata ?, and 7'. striata, as well as Plannlina turgida, 

 thus giving a common character to all these rock formations; 

 and this character becomes the more important, when we con- 

 siiier that these forms are the most numerous, and in fact are 

 the chief constituents of the chalk*. 



* The Polythalainian forms which Mr. I^onsdale noticed in the Englisli 

 chalk in 1837 as visible to the naked e^e, and amounting to 1000 in one 

 pound of the chalk, and which, with Mr. Ljell, he has named Lenticulina 

 and Discurt}is-\, appear, judging by ihe figures, to be referable to Rotalia 

 ornata and R.globtdosa, including j)erliaps fragments o\ Textularia gtobulosa. 



I may here remark, that my continued researches on the Polythalamia of 

 the chalk have convinced me, that very frequently in the earthy coating of 



t Dr. Buckland's Bridgewater Treatise, 2nd Eilition, vol. i. p. 448. 1 837. 

 Lyell's Elements of Geology, 1838. 



