Cir. XXVH.] IN OLDER ROCKS. 457 



trod the surface of this planet. So fixed was this idea in the minds of the 

 majority of naturalists, that, when at length the Stonesfield Mammalia 

 awoke from a slumber of three or four great periods, the apparition failed 

 to make them renounce their creed. 



" Unwilling I my lips unclose — 

 Leave, oh, leave me to repose." 



First, the antiquity of the rock was called in question ; and then the mam- 

 malian character of the relics. Even long after all controversy was set at 

 ret.t on these points, the real import of the new revelation, as bearing on 

 the doctrine of progressive development, was far from being duly appre- 

 ciated. 



It is clear that the first two or three species, encountered in any country 

 or in the rocks of any epoch, cannot be taken as a type or standard for 

 measuring the grade of organization of any terrestrial fauna, ancient or 

 modern. Suppose that the two or three oolitic species first brought to 

 fight had really been all marsupial, as was for a time erroneously im- 

 agined, this would not have borne out the inference which some attempted 

 to deduce from it, namely, that the time had not yet come for the crea- 

 tion of the placental tribes. Or r if when some monodelph were at last 

 actually recognized (at Stonesfield), they happened to be of diminutive 

 size, and to belong to the insectivora, we are not entitled to deduce from 

 such data that the oolitic fauna ranked low in the general scale, as the 

 insectivora may do in an existing fauna. The real significance of the dis- 

 coveries alluded to arises from the aid they afford us in estimating the true 

 value of negative evidence, when brought to bear on certain speculative 

 questions. Every zoologist will admit that between the first creation and 

 the final extinction of any one of the five* oolitic mammalia now known 

 there were many successive generations ; and, if the geographical range 

 of each species was limited (which we have no right to assume), still 

 there must have been several hundred individuals in each generation, 

 and probably, when the species reached its maximum, several thousands. 

 When, therefore, we encounter for the first time in 1854 two or three 

 jaws of a Spalacotherium in the Purbeck limestone, after countless speci- 

 mens of Mollusca and Crustacea, and hundreds of insects, fish, and rep- 

 tiles had been previously collected from the same beds, we are not simply 

 taught that these individual quadrupeds flourished at the era in question, 

 but that thousands, perhaps hundreds of thousands, of the same species 

 peopled the rand without leaving behind them any trace of their exist- 

 ence, whether in the shape of fossil bones or footprints ; or, if they left 

 any traces, these have eluded a long and most persevering search. 



Moreover, we must never forget how many of the dates given in the 



* I had written four, but while this sheet was passing through the press 

 (Sept. 26, 1854) the discovery of another species of insectivorous mammal from 

 Stonesfield was announced to the British Association at Liverpool by Mr. Charles- 

 worth, who has given to it the name of Stereognathus ooliticus. It is more than 

 twice the size of any of the species previously obtained from the same formation, 

 We have now, therefore, including the recently found Spalacotherium of Pur- 

 beck (see p. 295), five British mammalia from the oolite. 



