Prestwich's two objections are (1) the data of astronomy, and (2) "the difficulty of conceiving that man could have existed for 80,000 or 100,000 years without change and without progress." The former is "only one degree less mischievous than the theological prepossession." However, Prestwich has some "facts" as well as prepossessions, such as "the rapid advance of the glaciers of Greenland,"[98] which does not accord with the generalization from the Swiss glaciers;[99] and the quicker erosion of river valleys, due to a greater rainfall; facts which, however, are met by "a _minute description_ of the successive changes by which in post-glacial time the Mersey valley and estuary were brought into their present condition, with an estimate of the time they may have required;" which is "in round numbers 60,000 years," as opposed to Prestwich's 10,000 or 8,000. [100] The 200,000 years for the ice-age depends chiefly on Croll's theory of secular variation of the earth's orbitular eccentricity; but we are told it is open to the "objection that it requires us to assume a periodical succession of glacial epochs" of which two or three "must have occurred during each of the great geological epochs. [101] This is opposed to geological evidence." "'Not proven' is the verdict which most geologists would return." "The confidence with which Croll's theory was first received has been a good deal shaken." "We have to fall back, therefore, on the geological evidence of deposition and denudation ... in any attempt to decide between the 200,000 years of Lyell and the 20,000 years of Prestwich." [102] As to his arguments based on ancient human remains, their value depends first on the accuracy of his geological conclusions, and then on preclusion of all possibility of the conveyance of the remains from upper strata to lower; on the certainty, moreover, of traces of design in many of the would-be miocene or tertiary flint instruments (which Prestwich is doubtful about).[103] He takes care not to tell us that the Carstadt skull which gives name to a race, is a very doubtfully genuine relic of one hundred and thirty years old, whose history is most dubious. His evidence for the absence of the slightest approximation to the simian type even in the oldest relics is cheering to the theologian, though it loses its value when we know it is in the interests of his foregone conclusions as to the unspeakable antiquity of man. The Nampe image, the oldest relic yet discovered, "revolutionizes our conception of this early palaeolithic age," being a "more artistic and better representation of the human form than the little idols of many comparatively modern and civilized people," very like those in Mexico, "believed to be not much older than the date of the Spanish conquest"--"and in truth, I believe, contemporaneous." [104]