304 



the trails of aquatic animals, or even ripple-marks. Carruthers is disposed 

 to regard the structure which he has called Nematophycus, from the 

 Lower Erian or Upper Silurian beds of Canada, as the earliest algoid 

 remains or impressions which have come down to us. The true nature 

 of the tracings in the still earlier Laurentian rocks known as Eozoon 

 canadense is still a subject of controversy with palaeontologists and 

 petrologists. 



Coming down to more recent periods, the organisms described as 

 Chondrites and Confervites, found in the Cretaceous beds, were possibly 

 algae allied to the Confervaceae, and are thought by some to have had 

 a large effect in the precipitation of chalk from sea water, from the great 

 quantity of carbonic acid which they removed. From nodules in the 

 Pleistocene of Canada, Dawson obtains remains which he places under 

 genera allied to Ulva or Fucus, and possibly also to Laminaria. Various 

 other remains, sometimes of gigantic size, found in strata extending 

 over a very wide geological range, are referred by Saporta and others to 

 algae allied to the Laminariaceae and Fucaceae ; but the evidence is 

 generally too imperfect to justify a settled conclusion on the subject. 



Of the calcareous remains of algae which have come down to us, the 

 most remarkable are those described by Munier-Chalmas, including 

 more than fifty genera, which he refers to the Siphonocladaceae, mostly 

 found in the Triassic, Jurassic, Cretaceous, and Tertiary strata. The 

 calcareous skeleton contains hollow chambers and canals where the rays 

 and the organs of reproduction were seated in life, rendering them very 

 . liable to be mistaken for the remains of Foraminifera, under which 

 class of animals many of them have been placed by palaeontologists. 

 Among these is the genus Ovulites from the Eocene. 



LITERATURE. 



Balfour Introduction to Palaeontological Botany, 1872. 



Carruthers - (Nematophycus) Monthly Microscopical Journal, 1872, p. 208. 



Munier-Chalmas Comptes Rendus, 1877, P- 814; Bull. Soc. Geol. France, 1881, 



p. 661. 



Saporta Les organismes problematiques des anciennes mers, 1884. 

 Reinsch Micro-paleeophy tologia, 1 884. 

 Nathorst Nouvelles observations sur des traces d'animaux et autres phenomenes 



d'origine purement mecanique decrits comme Algues fossiles, 1886. 

 Delgado Etudes sur les Bilobites, 1886, 1888. 

 Dawson Geological History of Plants, 1888. 

 (See also under Fossil Vascular Cryptogams.) 



