I860.] Geology and Palceontology. 109 



described palseontologically, and selecting those that best illustrate 

 the several conditions of mineralization, he has arranged them into a 

 very good paper, forming a capital basis for future researches on the 

 general subject of fossilization. He has also done more than this 

 for the special subject of the West Indian fossil corals, having 

 determined and denned the following varieties of mineralization, 

 namely, calcareous, siliceous, siliceous and crystalline, siliceous and 

 destructive, siliceous cast, calcareo-siliceous, calcareo-siliceous and 

 destructive, and calcareo-siliceous cast. 



One very curious result in reference to the destruction and preser- 

 vation of anatomical details has been arrived at by the author, and is 

 thus stated : — " It would appear to be a rule that the minuter 

 structural details of corals are best preserved when the animal tissues 

 have been well washed out by the sea, and that the loss of these 

 details bears a relation to the length of time the decomposing soft 

 membranes remain in contact with the sclerenchyma." 



Dr. Duncan's memoir is rich in remarkable cases of silicification, 

 each one of which might form the basis of a good paper on the theoiy 

 of the subject by an experienced chemist ; in this place, however, we 

 pass them by, as well as the author's own views on specially interest- 

 ing cases, but we cannot help giving his chief and most important 

 conclusion in his own words : — " Silica, whether homogeneous, granu- 

 lar, or crystalline, does not appear to be deposited at first in the 

 interspaces of corals, but replaces a salt of lime which was infiltrated 

 partly in solution, or partly in a state of mechanical suspension in a 

 compound fluid. The replacement does not commence until the salt 

 of lime has acquired a certain density, and it occurs first of all in the 

 central parts of the loculi, in the form of granular points." 



4. The oldest known Mammal. — Mr. Boyd Dawkins's paper " On the 

 Rhastic Beds and White Lias of Western and Central Somerset, and 

 on the Discovery of a new Fossil Mammal in the Grey Marlstones 

 beneath the Bone-bed," is a valuable contribution to the literature of 

 the strata treated of, and adds greatly to our knowledge of them as 

 they occur in Somersetshire ; but the chief interest of the paper is 

 centred in the latter part, in which is described a worn premolar 

 tooth of a new Mammal, called Hypsiprymnopsis Bhaiticus by Mr. 

 Dawkins, and supposed to be the oldest known representative of the 

 Mammalia. 



The tooth has an oblong crown, the summit being obliquely worn, 

 and exhibiting on its higher side, which adheres to the stone (see 

 Fig. 3), two isolated involutions of enamel on that portion of the tooth 

 that is supported by the posterior fang. In front of these are two 

 wider and less prominent folds, and there may have been another on* 

 the anterior corner, which has unfortunately been broken by the 

 waves. 



It will be seen from Fig. 5, that the worn premolar tooth of 

 Hypsip-ymnus minor exhibits a very similar appearance, the traces of 

 the plications being no more prominent than in the fossil, although in 

 the unworn tooth of the same species (Fig. 4) they form so marked a 

 feature. Again, on the lower or outer side of the former, as in the 



