XXU INTRODtrCTIOH'. 



fragments of gj-mnospcrms and ferns, though he found and 

 described several woods with petrified structure. Penhallow 

 contiaued the investigation of the impressions, and also treated 

 of Gymnospermic woods, but his most interesting addition 

 to the Flora was that of Osmundites with its internal anatomy 

 (iy02A). 



United States. — The enormous extent of the Cretaceous 

 deposits in this country, and the richness of the beds in plant- 

 impressions, have led man)' workers to investigate them. The 

 list of American publications is indeed lengthy, and instead of 

 summarising them here, it may be better to refer to Ward's 

 exhaustive paper (Ward, 1889, pp. 834-926) for an account of 

 the earlier literature. Knowlton's Catalogue (1898) of the 

 American Tertiary and Cretaceous plants brings the lists more 

 up to date. Since this time the most active workers have been 

 Berry (1901-1910), Xnowlton (1889-1910), HoUick (1892- 

 1910), HoUick & Jeffrey (1909), and finally Wieland, whose 

 publications are almost confined +0 the Cycadophyta, which are 

 principally froai older deposits but afford results of great im- 

 portance in a consideration of the Cretaceous Flora. The 

 majority of the American specipaens are in the form of leaf- 

 impressions, and they occur eastwards in the clays and shales, 

 and westwards in the great Coal-bearing series. Several 

 species of petrified (silicified) wood have been described by 

 Knowlton ; but the most important plants with their internal 

 anatomy are those with which HoUick & Jeffrey and their 

 pupils have made the locality of Ftaten Island famous. These 

 plants, preserved in the fine clay (Amboy Clay), are not exactly 

 petrifactions in the ordinary sense, but are fragments in which 

 the internal parts are fairly well preserved, much as they would 

 be in peat. Dr. Berry's important monograph on the Lower 

 Cretaceous plants of America has now appeared. Unfortunately 

 the present work only includes literature and species appearing 

 before the end of 1910, and as so much of the present volume 

 was in type before Dr. Berry's work was published, it is im- 

 possible to include his results. 



Mexico. — Petrifactions of wood have been described by Felix 

 & Nathorst from the State of Oaxaca ; and Steinmann (1899) 

 recorded and described interesting Siphonacejs with their 

 structure well preserved, 



