75 



brought to light the curious and important fact, that though 

 calcareous matter constituted the great bulk of the fossil body, 

 the tissues themselves were siliceous, and consequently proof 

 against the action of the acid. It moreover put beyond all 

 doubt the correctness of Prof. Phillips' location of these fossils 

 among the sponges, their structure thus cleared of extraneous 

 matter being so obviously spongious that it was impossible to 

 mistake it.* 



The process of mineralization has here in every case extended 

 to the whole of the original organism, external to which there 

 is no deposition of either sihceous or calcareous matter. This 

 condition of completeness, so unusual in the Zoophytes of 

 the Chalk, and the facility with which their internal organis- 

 ation can be displayed, do not, however, promise to yield satis- 

 factory data on which to base specific characters for the Brid- 

 lington Sponges, but rather to demonstrate that among these 

 fossils even very remote types of form, by a series of transitional 

 links, may so insensibly merge into each other, as to render 

 hopeless any attempt to lay down definitions of species which 

 shall not rather perplex than assist the Geological student. 



Prof. Phillips, in his ' Geology of Yorkshire,' has figured cha- 

 racteristic examples of the more remarkable forms presented by 

 the fossils imder consideration. Including under the general 

 name " Spongia," Ventriculites and Siphonia, he enimierates 

 in all ten species, but his figvires are not accompanied with any 

 explanatory or descriptive details. To the above ten species 

 Mr. J. E. Leef has proposed to add eight more, but this author 

 in the nomenclature of his species adopts the genera Siphonia, 

 Spongia and Udotea. Putting aside the Spongia cribrosa, 

 porosa, lajvis, and Benettia? of the ' Geology of Yorkshire,' the 

 Udotea cancellata and Spongia spinosa of Lee, it appears to 



• It is hardlj necessary to remark that tlie time and pains spent in the 

 the attempt to remove bv mechanical means the hard chalk from the surface of the 

 Bridlington Sponges, may in most cases be now saved by the emplojonent of acid. 

 It requires however some practice, and the exercise of judgment, to ensure success 

 in its application, and the possessors of these fossils would do well not to com- 

 mence witli experimenting upon their best specimens. 



+ Magazine of Natural History, vol. •?, new series, page 10. 



