^6 



minute organisms occur, so that whole lakes have been 

 filled up by them, and deposits, composed of little else 

 than the remains of infusorial animalcula, have been mea- 

 sured to as much as 14 feet in thickness.* 



Further, that in the genuine Tertiary Strata^ as, for 

 example, the Eocene Sands of Grignon, the proportion of 

 minute Foraminifera, which is mixed with the common sand, 

 is enormous.f 



Again, that in secondary strata, especially in the chalky 

 minute Foraminifera and minute Infusoria abound, so that 

 whole beds appear to consist of little else, especially in the 

 South of England and in the North of Germany.^ 



It has been also ascertained, that in the secondary strata 

 below the chalk, particularly in the Oolites of Yorkshire 

 and Stonesfield, many of the Foraminifera occur ; and it 

 is a result of my own researches, that in the mountain 

 limestone they are not rare, and that the limestone of 

 South Devon and the silurian limestones contain traces of 

 this widely diffused class of Microzoa. 



I will now briefly notice, commencing with the Mountain 

 Limestone, the most frequent of the minute organized bodies, 

 which are revealed by the microscope, in those parts of the 

 calcareous deposits of Yorkshire, which, to the unassisted 

 eye, appear to be devoid of organization. 



Of this rock it will be sufficient to notice two varieties, 

 the oolitic and the compact. In the former it is common 

 to find, in the centre of the grains or ova, minute 

 Foraminifera, bits of coral, small joints of Encrinites, and 

 small Goniatites. 



In the compact rock we find precisely the same things, 

 as Foraminifera, small Milleporidse, minute Cyathophylla, 

 minute Calamoporse, Crinoidal joints, and Goniatites. They 



* Ehrenberg. t D'Orbigny, &c. \ Ehrenberg. Reade. Mantell. 



