FLORA OF THE OOLITIC EPOCH. 83 



fossil from tlie Oolite of Yorkshire (Carrutliers, Geol. Mag. 

 yi. 91). Araucarites sph^roearpus (Figs. 83, 84, 85) is found 

 in the inferior Oolite, and separate scales of Araucarian fruits 

 occur in the Oolitic shales of Yorkshire (Araucarites Phil- 

 lipsii, Plate II. Fig. 11), and in the " slate " at Stonesfield (A. 

 Brodiei, Plate II. Fig. 10). The upper Oolite at Portland con- 

 tains an interesting bed, about a foot in thickness, of a dark 

 brown substance. This is the Dirt-bed (Fig. 86) made up of 

 black loam, which, during the Purbeck period, formed a sur- 

 face soil which was penetrated by the roots of trees, frag- 

 ments of whose stems are now found in it fossilised. These 

 consist of an assemblage of silicified stumps or stools of large 

 trees, from 1-3 feet high, standing in their original position, 



Fig. 86. Fig. 87. 



with the roots remaining attached to them, and still pene- 

 trating the earth in which they grew. Besides the erect trunks 

 many stems haye been broken and throAvn down, and are buried 

 in a horizontal position in the bed. They belong to Conifera) 

 and Cycadace^. One of these is Mantellia nidiformis, shown in 

 Fig. 87. Carpolithes conicus and C. Bucklandi are fruits found 

 in the Oolite. Some look upon them as fruits of palms. 



Fig. 86. The Dirt-hed of the Island of Portland, containing stumps 

 of fossil Cycadacese in an erect position. 



Fig. 87. Cycadoidea megalophylla (Mantellia nidiformis of Brong- 

 niart), a subglobose depressed trunk, with a concave apex, and with 

 the remains of the petioles disposed in a spiral manner, the markings 

 being transversely elliptical. It is found in the Oolite of the Island 

 of Portland, in a silicified state. 



