Proceedings of the British Association. 139 



miles together a deposit of the coprolitic matter of the great saurians 

 of the period, a formation which could only have taken place, tran- 

 quilly, during the lives of many generations of those animals. In a 

 newer part of the series, the rocks constituting Portland Island, we 

 find, resting on beds of marine limestone, layers of vegetable soil 

 containing large prostrate trunks of dicotyledonous trees, and por- 

 tions of their branches remaining upright, and fixed in the earth by 

 their roots ; and trunks of plants resembling the recent Zamia, stand- 

 ing where they grew, but silicified, and covered up with beds of 

 fresh-water limestone. Here, again, a few feet of strata represent a 

 period of time in which the sea was converted into dry land, the land 

 overgrown by forests ; and this again became a fresh-water lake, 

 inhabited by shells allied to species now existing. To the single 

 stratum, therefore, where these trees were found, belongs a period of 

 time sufficient for the growth of a forest. Time would fail me to 

 tell the numerous changes of physical condition, accompanied with 

 corresponding changes in animal organization, which characterize 

 every division of the cretaceous and tertiary strata. The Dean of 

 York, indeed, says, that " little remained for them to inclose, and 

 little is inclosed within them." Here, again, is a strange ignorance 

 of notorious facts, for these are the very strata in which the traces 

 of organic life are most varied and abundant. The conclusions of 

 geologists would indeed be vain if founded on such irrational guesses 

 and absurd hypotheses ; but by a steady and humble study of nature, 

 in a subject so vast and comprehensive, we could make but little 

 progress, did we not call in the aid of the zoologist, the botanist, 

 and the chemist, and, paying the utmost respect to their opinions, 

 regulate our conclusions by their evidence. In determining the 

 succession of the strata, or any other problem in our science, we 

 must be content to ascend, step by step, from small assemblages of 

 facts, to higher generalizations, until we obtain the whole sequence. 

 With regard to the succession of animal life, the evidence is so 

 conclusive that no naturalist or competent observer will now deny 

 that new species have continually appeared — not by the transmuta- 

 tion of those before existing — but by the repeated operation of 

 creative power. In his ordinary dealings with the natural world 

 God works by second causes ; so that one natural phenomenon may 



