CENOZOIC ERA. AGE OF MAMMALS. 371 



tion the conditions of things which prevailed in Tertiary 

 times : 



1. In the Miocene fresh-water deposit of Oeiiingen, a 

 layer two feet thick is black with the remains of insects. 

 It is also full of leaves. About nine hundred species of 

 insects and five hunclred species of plants have been made 

 out. The larger number of insects are beetles and ants. 

 We may imagine that in Miocene times there was at 

 Oeningen a lake surrounded with a thick forest, whose 

 leaves were scattered on the waters and cast upon the 

 shore. Beetles and flying ants, essaying to fly over the 

 lake, were beaten down by the winds and also cast on 

 the shore. These remains were covered up by mud, and 

 thus preserved. 



2. On the shores of the Baltic, bits of amber, derived 

 from Miocene strata outcropping beneath the water, are 

 continually thrown up by the action of the waves. In 

 these are found, sealed up, and in transparent pieces 

 clearly visible, great numbers of insects, often in an 

 exquisitely perfect state of preservation. About eight 

 hundred species of insects and one hundred and fifty 

 species of plants have been described. The insects are 

 mostly winged ants and flies. Amber is known to be the 

 fossil gum of a pine (Pinus succinifer). We may imagine, 

 then, that in Miocene times, in the region now occupied 

 by the southern Baltic, there was a forest, among the 

 trees of which the Pinus succinifer abounded. From 

 these trees a semi-liquid, sticky gum exuded in tears, on 

 which insects alighting stuck fast, and were covered by 

 later exudations. 



3. In Auvergne, France, there is a Miocene fresh-water 

 deposit, one layer of which, two to three feet thick, is 

 almost wholly composed of the cast-off cases (indusia) of 

 caddis-worms, and is therefore called indusial limestone. 

 The caddis-worm (larva of the caddis-fly) of to-day is a 

 wingless creature, living wholly in the water. It has the 



