and other Siliceous Bodies. 1 1 



face of the original mass, small portions of the tissue are some- 

 times observed in so perfect a state as almost to deceive the 

 observer into believing them to be fragments of recent sponges. 

 In some parts of the mass, especially near that which is in 

 the finest state of preservation, parts of the structure may ge- 

 nerally be seen in all the intermediate stages between perfect 

 preservation and nearly complete decomposition, where the 

 organic tissues have resolved themselves into a shapeless 

 mass, only to be recognised as formerly having belonged to 

 the sponge by the aid of the surrounding, connected and less 

 decomposed parts of the animal structure. 



The siliceous matter in which these remains are imbedded 

 usually presents a clear and frequently a crystalline aspect, 

 while the remains of the organized matter is strongly tinted 

 with colour : bright red, brown and ochreous yellow are the 

 prevailing colours, but occasionally the fibre is milk white or 

 bright green. Sometimes the interior of the tubular fibre 

 only is filled with colouring matter, while the sides are of a 

 semipellucid or milky white ; in others the whole of the fibre 

 is impregnated with it. The colouring matter is generally 

 confined within the bounds of the animal tissue, leaving its 

 surface smooth and uninterrupted ; but occasionally the fibre 

 is not only completely charged with it, but its surface is also 

 slightly encrusted by it. 



These are the usual characters presented by the greater 

 portion of the moss agates of Oberstein and other parts of 

 Germany. 



It would be taxing the patience of the reader to too great 

 an extent if I were to attempt to describe the whole of these 

 siliceous bodies that I have subjected to examination ; I shall 

 therefore confine myself to a detailed description of a few of 

 the most characteristic specimens, and especially to those 

 which afford the strongest and most perfect evidence of their 

 organic origin. 



The first of these specimens is a moss agate, said to be from 

 Sicily. The structure of the sponge tubuli is very obscure in 

 the greater part of the mass, but at the margin of the specimen 

 the tubes are in as perfect a state of preservation as if they were 

 those of a recent sponge immersed in Canada balsam ; in this 

 state they are represented in PI. I. fig. 1. anastomosing pre- 

 cisely in the same manner as those of the Mediterranean 

 sponge, and where they have been divided at the surface of 

 the specimen they are frequently observed to be hollow. No 

 spicula are present, but it is evident that it was a true kera- 

 tose sponge. The greater part of the specimen consists of in- 

 numerable bright red fibres of nearly an uniform diameter, 

 ramifying in every direction, frequently terminating as if 



