316 HISTORICAL PALEONTOLOGY. 



similar to some of the existing European forms. Lastly, the 

 Eocene deposits have yielded more or less satisfactory evi- 

 dence of the existence in Europe at this period of examples of 

 the orders of the Gnawing Mammals (Rodentia), the Insect- 

 eating Mammals (Insectivora), and the Monkeys (Quadru- 

 mana). * 



CHAPTER XIX. 

 THE MIOCENE PERIOD. 



The Miocene rocks comprise those Tertiary deposits which 

 contain less than about 35 per cent of existing species of shells 

 (Molluscd), and more than 5 per cent or those deposits in 

 which the proportion of living shells is less than of extinct 

 species. They are divisible into a Lower Miocene (Oligocene) 

 and an Upper Miocene series. 



In Britain, the Miocene rocks are very poorly developed, 

 one of their leading developments being at Bovey Tracy in 

 Devonshire, where there occur sands, clays, and beds of lignite 

 or imperfect coal. These strata certain numerous plants, 

 amongst which are Vines, Figs, the Cinnamon-tree, Palms, 

 and many Conifers, especially those belonging to the genus 

 Sequoia (the "Red-woods"). These Bovey Tracy lignites are 

 of Lower Miocene age, and they are lacustrine in origin. Also 

 of Lower Miocene age are the so-called " Hempstead Beds " 

 of Yarmouth in the Isle of Wight. These attain a thickness of 

 less than 200 feet, and are shown by their numerous fossils to 

 be principally a true marine formation. Lastly, the Duke of 

 Argyll, in 1851, showed that there existed at Ardtun, in the 

 island of Mull, certain Tertiary strata containing numerous 

 remains of plants ; and these also are now regarded as belong- 

 ing to the Lower Miocene. 



* A short list of the more important works relating to the Eocene 

 rocks and fossils will be given after all the Tertiary deposits have been 

 treated of. 



