RELATION OF BIOLOGY TO GEOLOGICAL INVESTIGATION. 357 



such as would be likely to be preserved in a fossil state. Therefore it 

 is not to be expected that fossil remains referable to the Ccelenterata 

 will be found in any formation of fresh -water origin. 



The marine subclasses Siphonophora, Discophora, and Lucernarida, 

 as well as many members of the class Actinozoa, are also all destitute 

 of such skeletal parts as are likely to long- resist decomposition after 

 the death of the animal. It is an interesting - fact that unmistakable 

 imprints of the bodies of Codenterata belonging or related to the jelly- 

 fishes have been found in certain geological strata composed of ex- 

 tremely hue sediments; but, as a rule, the geologists can not hope to 

 discover any fossil traces of animals which in life were not furnished 

 with such skeletal or integumentary parts as would resist the decompo- 

 sition of their soft parts after death. While the bodies of many of the 

 Ccelenterata are wholly of this soft character, a large proportion of them 

 are furnished with stony skeletal parts, the most conspicuous examples 

 of which are the numerous kinds of corals. Others are furnished with 

 corneous or chitinous coverings or supports which are sometimes found 

 fossilized. So characteristic; are these Actinozoa of marine waters that 

 the geologist does not hesitate to accept as of marine origin any forma- 

 tion containing fossil corals, which are the skeletal parts of such 

 animals. 



PROTOZOA. 



Of the Protozoa only the orders Foraminifera, Eadiolaria, and Spon- 

 gida need be mentioned in this review, because only representatives of 

 these orders secrete such hard parts as are likely to be preserved in a 

 fossil state. Much the greater portion of the Protozoa are microscopic- 

 ally minute, but the sponges and some other forms are frequently of 

 large size. The Protozoa live in both fresh and marine waters, but 

 they are so very much more abundant in the latter that the discovery 

 of their remains in a geological formation is usually taken as indicat- 

 ing its marine origin. 



PLANTS. 



( Jompared with the fossil remains of animals very little direct infor- 

 mation can be obtained from those of plants as to the character of the 

 water in which the formations containing them were deposited. 



The siliceous remains of diatoms often constitute layers of consider- 

 able thickness among the sedimentary rocks, but because they are 

 found in both marine and nonmarine deposits, and because of the 

 special character of their classification, they are not definitely referred 

 to in these discussions. 



All seaweeds or marine plants are far more simple in structure than 

 land plants and their composition is such as to insure their rapid de- 

 composition. This character has prevented their fossilization in the 

 sediments of formerly existing seas in such a condition as to be of any 

 considerable value in paleontological study. The case is somewhat 



