GEOLOGY. 299 



in the third fishes commence, and brachiapccls have become rare. In the 

 uppermost stage the community of species is reduced to the trilobites, 

 and the entire fauna is poverty stricken. Traces of vegetables also indi- 

 cate some considerable changes in the conditions of the sea-beds. 



M. Barrande definitely settles the fact, that the trilobite undergoes 

 metamorphoses in the course of its existence as an individual. He has 

 demonstrated the fact in the case of sixteen genera and twenty-eight 

 species. The degree of change is variable, and its intensity is comparable 

 with the phenomena in existing Crustacea. Among other points, M. Bar- 

 rande has made out the probable eggs of these animals. As to their mode 

 of life, he is opposed to the opinion that they lived in shallow water along 

 the coast, and distinctly pronounces against the supposition of their para- 

 sitic nature. 



Prof. Forbes expresses it as his opinion, in regard to the extinction of 

 species in geological time, that every year's research makes it more and 

 more evident that it is simply the result of the influence of physical 

 changes in specific arrears, and depends xipon no law of inherent limitation 

 of power to exist in time. 



M. de Archiac and Haime are about to publish an extensive work on 

 the fossil animals of the nummulitic rocks of India. 



The enormous increase of paloeontological observations may be meas- 

 ured by a comparison between the number of British fossils catalogued a 

 few years since and the number at present recognized. The number of 

 plants recorded in 1843 was 510 ; in 1853, 652 are cited. The increase is 

 chiefly among the Mesozoic and Tertiary types. The Foramenifera, of 

 which 82 were mentioned in the list of 1843, has increased to more than 

 168. Of Zoophytes, the number has increased from 183 to 438 ; of Bryozoa, 

 117 new species have been added; of Echinodermata, 213 ; of Cirripeclia, 

 21; Crustacea, about 150 ; Brachiopoda, 200 new species; of Monomya- 

 rian Bivalve's, about 250 ; and of fossil insects, the number has also largely 

 increased. This increase it must be remembered pertains only to the 

 British Islands. 



Says Prof. Forbes, in his address before the London Geological Society, 

 """Every geologist, whose studies have been equally or nearly directed to 

 the organic phenomena of the three great sections of time usually received, 

 Paleozoic, Mesozoic and Tertiary, cannot fail to have been struck with the 

 greater value of the difference between the first, or oldest section, and the 

 two newer divisions, taken together, than between the first and mid- 

 dle terms, and between the latter and the last. The degree of organic dif- 

 ference between the Upper Mesozoic and the Lower Tertiary epochs is 

 rather more, but only slightly more, than the degree of difference between 

 the lower and upper sections of the great Mesozoic period. But the gap 

 between Palaeozoic and Mesozoic, although the link be not altogether 

 broken, is vastly greater than at any other of the many gaps in the known 

 series of formations. I am one of those who hold, a priori, that all gaps 

 are local, and that there is a probability at some future time of our dis- 



