[footnote]*\"leplusgrandservicequ’onpuisserendrealascienceestd’yfaireplacenetteavantd’yrienconstruire。\"——CUVIER
Theevidenceonwhichsuchconclusionsarebasedisoftwokinds，negativeandpositive。Thevalueofnegativeevidence，inconnectionwiththisinquiry，hasbeensofullyandclearlydiscussedinanaddressfromthechairofthisSociety*，whichnoneofushaveforgotten，thatnothingneedatpresentbesaidaboutit；themore，astheconsiderationswhichhavebeenlaidbeforeyouhavecertainlynottendedtoincreaseyourestimationofsuchevidence。Itwillbepreferabletoturntothepositivefactsofpaleontology，andtoinquirewhattheytellus。
[footnote]*AnniversaryAddressfor1851，’Quart。Journ。
Geol。Soc。’vol。vii。
Weareallaccustomedtospeakofthenumberandtheextentofthechangesinthelivingpopulationoftheglobeduringgeologicaltimeassomethingenormous：andindeedtheyareso，ifweregardonlythenegativedifferenceswhichseparatetheolderrocksfromthemoremodern，andifwelookuponspecificandgenericchangesasgreatchanges，whichfromonepointofview，theytrulyare。Butleavingthenegativedifferencesoutofconsideration，andlookingonlyatthepositivedatafurnishedbythefossilworldfromabroaderpointofview——fromthatofthecomparativeanatomistwhohasmadethestudyofthegreatermodificationsofanimalformhischiefbusiness——asurpriseofanotherkinddawnsuponthemind；andunder’this’aspectthesmallnessofthetotalchangebecomesasastonishingaswasitsgreatnessundertheother。