Vast lapse of time between the close of the Palæozoic and beginning of the Tertiary Volcanic Eruptions--Prolonged Volcanic Quiescence--Progress of Investigation among the Tertiary Volcanic Series of Britain. From the evidence which has been led in the foregoing chapters it is clear that during the later stages of the Palæozoic period there was a gradual enfeeblement of volcanic vigour over the area of the British Isles. When the last puys of the Permian series became extinct a remarkable volcanic quiescence settled down on the region. This interval of rest lasted throughout the whole of the long succession of the Mesozoic ages. Though the geological record of this section of geological time is singularly complete in Britain, not a single vestige has yet been found in it of any contemporaneous eruption. And what is true of this country is, on the whole, true of the entire European continent. With some trifling exceptions there were no volcanoes in Europe, so far as we know, during the enormous lapse of time between the last of the Palæozoic and the earliest of the Tertiary eruptions. When the geologist attempts to form an estimate of the chronological value of this interval of time he is soon lost in bewilderment over its obvious vastness, and the impossibility of discovering any standards of measurement by which to reckon its duration. On the one hand, he sees that it lasted long enough to admit of the gradual elaboration of many thousands of feet of various sedimentary deposits, which, from their remarkable diversities of character, were evidently accumulated, on the whole, with extreme slowness and amidst many geographical vicissitudes. On the other hand, he perceives that the interval sufficed to bring about an entire change in the fauna and flora of the globe. Indeed, the more he investigates the details of this biological transformation, the more he is impressed with the length of time that it must have required. For it is not merely one complete change, but a multifold succession of changes. The stratigraphical records of the long array of geological periods over which it was spread show that the biological evolution advanced through a vast series of species, genera and orders which one by one appeared and disappeared.