174 PEOF. J. W. JTJDD ON THE OLIGOCENE 



SO strikingly exhibited in the Alps and Himalayas and the other 

 great ranges which constitnte the axis of the eastern continent. 

 At the same time, too, began those volcanic outbursts along lines 

 parallel to this axis, which attained their climax in the Miocene 

 period, and have not yet died out at the present day. 



The Oligocene was a period at which, as we have seen, many os- 

 cillations in the level of the land and sea took place in this part of 

 the globe, elevation and subsidence alternating with one another 

 again and again. Hence we find the thickness of the several de- 

 posits exhibiting great variations within very short distances. In 

 eastern Europe (Hungary and Trans5dvania) the Oligocene strata 

 attain a thickness of from 2000 to 3000 feet, and contain numerous 

 beds of coal, one of which, in the Tsilthal, measures no less than 

 90 feet. But in Northern and Western Europe the Oligocene is re- 

 presented by a series of delta deposits of much less considerable 

 thickness. As, however, we approach the great mountain axis, 

 where the maximum amount of movement has taken place, we find 

 that deposits of enormous thickness have been accumulated, as in 

 Bavaria, Switzerland, and Northern Italy, where beds of this age 

 attain a thickness of from 10,000 to 12,000 feet. 



That the Oligocene must represent a period of enormous duration 

 we cannot, after what has been stated concerning the thickness of 

 the deposits, for one moment doubt. And this conclusion is fully 

 sustained when we come to studj^ the marine and terrestrial forms 

 of life which flourished while these strata were being accumulated. 

 The labours of Bejrich, Yon Konen, Sandberger, and others have 

 now made known to us a marine fauna consisting of several thou- 

 sands of species ; and this fauna is found to be clearly distinguished 

 alike from that of the Eocene below and that of the Miocene above. 

 The reasons why Lyell failed to recognize this great fauna and to 

 include it in his scheme of classification of the Tertiary strata, we 

 have already pointed out. The terrestrial fauna and flora of the 

 Oligocene is also as distinct from those of the Eocene and Miocene 

 respectively, as is the marine fauna ; and the characteristic Oligo- 

 cene terrestrial fauna and flora have been recognized, not only in the 

 Eastern continent, but in North America. 



That which has been asserted of the Oligocene formation gene- 

 rally, may be maintained with equal truth concerning its represen- 

 tatives in these islands, the fluvio-marine strata of the Hampshire 

 basin. These strata, although they unfortunately furnish only a 

 fragmentary record of the earlier portions of the Oligocene period, 

 are nevertheless between 800 and 900 feet in thickness. They con- 

 tain a marine fauna and a terrestrial fauna and flora agreeing in 

 the most perfect manner with those of the continental Oligocene ; 

 and, moreover, the great zones of life determined in the latter can, 

 as we have pointed out, be clearly recognized in the former. Like 

 the continental Oligocene strata, our fluvio-marine beds were evi- 

 dently deposited during a period of oscillation which followed the 

 long-continued submergence of the Eocene or Nummulitic, and pre- 

 ceded the final and most violent of those movements to which the 

 plication and metamorphism of the Alpine rocks bear such striking 



