BElfSTED — ON THE GEOLOGY OE MAIDSTONE. 



335 



shape and appearance very like an alcvonium. Some of the branches 

 of these fossils radiate from the central mass to a distance of 18 inches 

 (fig. 7), each branch ending with a thick knob, and I have seen as 

 many as twenty or thirty springing from a single stem. In some 

 instances the sponges are prostrate, in others erect, as in fig. 4, plate 

 xix. 



It is very rarely that shells are found in the stone of this group ; oc- 

 casionally a detached valve of a terebratula or of an oyster is seen. 

 The associated beds of hassock are very soft, and full of casts of 

 cylindrical stems ; the lowermost stone-bed is remarkably cavernous, 

 from the hassock below it being washed away, leaving the siliceous no- 

 dules standing out. 



In 1846 I discovered in these beds a saurian bone bearing a great 

 resemblance to the tibia of the Iguanodon ; but as only one end was 

 preserved, I cannot come to any certain determination of it. 



A second group of limestone now follows, of a light colour, and as- 

 sociated with hassock of a very good quality for building-purposes. 

 The first bed is sometimes 8 feet in thickness, and the stone excel- 

 lent for working up. The hassock ranges from 2 to 8 feet in thick- 

 ness, and is of a coarse texture. No traces of stem-casts have been 

 met with in this group. One of the most remarkable of the Lower 

 Greensand spongeoiis organisms is, however, so characteristic of it, 

 that in the course of twenty years' collecting I have not met with 

 this form in any of the other strata. During that period I have col- 

 lected a large number of specimens, showing a great variety of form 

 and condition, it being only from a very numerous and well-selected 

 series that a true conclusion as to their habits of growth and nature 

 can be drawn. These fossils are, I believe, a species of Siphonia. The 

 accompanying figures (PI. xvii. and xviii.) give numerous details of 

 the principal and the subsidiary parts. It appears to have had a cylin- 

 drical stem, with lobes at intervals in the course of its direction; the 

 lobes bulging out on one side more than on the other, and varying 

 much in size. They are generally rougher or more covered with pa- 

 pilla3 than the stem. Four, and even more, of these lobes have been 

 seen on a single stem, the apex or top of which general consists of a 

 nodule of siliceous sand, even when these sponges are embedded in 

 the limestone rock. In the accompanying plate (PL xvii.) the head 

 is composed of siliceous sand, the stem and lower lobe of calcareous 

 limestone of similar texture to the surrounding matrix. These con- 

 ditions were so common, that I was led to examine the structure of 

 the siliceous heads, and found that sponge-spicula3 were much more 

 abundant in them than in the stem and lower lobes, which invariably 

 partake more or less of the properties of the surrounding stone. 



These sandy or cherty heads or nodules sometimes contain a con- 

 tinuation of the stem and one of its lobes as a core within them. In 

 some specimens only an ordinary portion of the stem passes through ; 

 in others, these siliceous excrescences are permeated by numerous 

 smaller branches ramifying through them. These nodules are full of 

 sponge-spicuL'E, which are especially abundant round the stems and 



