36 AN INTRODUCTION TO THE STUDY OF FOSSILS 



Tertiary. On the Isle of Wight there are considerable deposits 

 of Oligocene fresh water limestone which are rich in remains 

 of Chara. 



2. Brown algae. — Examples are : — 



a. Fucus, the rock weed, common on rocks exposed between 

 tides. 



h. Laminaria, the large alga, devil's apron, etc., growing in 

 the deeper water beyond the low tide limits (Fig. ii, A). This 

 marine genus includes the largest plants known, some having 



huge trunk-like 

 stalks and reaching 

 a height of several 

 hundred feet. 



c. Sargassum of 

 the Sargasso seas. 



d. Nematophy- 

 cus, a large plant 

 w^hose fossilized 

 stems have been 

 found in the Silu- 

 rian and Devonian 

 of Europe and 

 America. In some 

 respects it resem- 

 bles the big Lami- 

 narian seaweeds of 

 the present, though 

 its exact relation- 

 ship cannot be de- 

 termined since its 

 microscopic struc- 

 ture is not pre- 

 served. 



There are no im- 

 portant lime-secreting genera among the brown algae. 



B 



Fig. 8. — A marine lime-secreting alga, Primicorallina 

 trentonensis Whitfield, from the Trenton limestone 

 (Middle Ordovician) of New York. Much of the 

 limestone where it occurs is made up of its remains. 

 A, a specimen showing the whorled arrangement of 

 the branchlets of the second order at a and those 

 of the third order at b. B, restoration of the entire 

 plant. (From Ruedemann.) 



