20 Missing Chapters of Geological History. 



Palaeozoic rocks show an approximation to those of the Secondary 

 period, is a fact to be understood only by tabulating and massing 

 the various details, already very numerous, on which a general 

 conclusion like this can be based. Thus, in comparing collec- 

 tions of fossils from the older divisions of the early period, as 

 lower Silurian with Devonian, we find that genera are repre- 

 sented by very few species, and that there are many species in 

 proportion to the number of specimens. In other words, there 

 is a great variety of type-forms, but a poverty of actual repre- 

 sentative forms. So again in the older rocks there is a prepon- 

 derance of Brachiopodous over other mollusca ; but in the Car- 

 boniferous groups the reverse is the case, especially with regard 

 to species ; though, if we estimate only the number of individual 

 specimens in collections, the Brachiopoda are still preponderant. 

 In the Permian rocks, few as the fossils are, they point to a con- 

 tinuance of the same change, and this in a marked manner. On 

 the whole, we may say, that the proportion of species to a genus 

 increases in all departments, not gradually and steadily, but 

 suddenly, on entering the Carboniferous period, and again on 

 entering the second stage of the great geological history. How 

 far the nature of the sea-bottom, and the increasing deposits of 

 calcareous matter in these parts of the world, may have affected 

 the matter, it is not easy at present to say ; but it hardly alters 

 the conclusions we have arrived at. 



There is no true strati graphical passage in England from Per- 

 mian to the New Ped Sandstone formation, for, even when not 

 unconformable, there is a distinct absence of some known mem- 

 ber. The whole of the New Red Sandstone (the oldest Secondary 

 formation) is also so exceedingly poor in fossils, in this country, 

 that to form any idea of the deposits that represent the extra- 

 ordinary break in the forms of life, it is necessary to borrow 

 from Continental experience. There these beds are abundantly 

 represented, and afford ample material for comparison. The St. 

 Cassian beds, in the Italian Alps, sometimes considered to overlie 

 the Muschelkalk, are the deposits that have chief relations with 

 Palseozoic rocks. They have yielded a large number of species, 

 of which the Brachiopoda are essentially of Palaeozoic types. Of 

 the other types of mollusca, many are common to the older and 

 newer periods. The general result is, that one-third of the 

 fossils are Palaeozoic, and two-thirds Secondary, in general ap- 

 pearance. The Muschelkalk is far more essentially Secondary, 

 and there has always been a doubt on the minds of geologists 

 as to the exact position of the remarkable beds from these 

 mountain districts. 



It is only the upper bed of the Triassic period, known as 

 the " bone bed," and long regarded as part of the Lias, that is 

 rich in fossils in our country. It was not, indeed, till 1860 



