513 



for example), occur also in the Portland-stone of Wiltsliire; another, 

 as Ostrea Marshii, is characteristic of the cornbrash in the same 

 county ; others pass downwards to the lias, as Orbicula reflexa and 

 Ammonites striatulus. If you consult the tables of organic remains 

 which Dr. Fitton has annexed to his excellent monograph on the 

 strata below the chalk, just published in our Transactions, (2nd Se- 

 ries, vol. iv. part 2.) you will see that a considerable number of 

 shells pass from the upper oolitic groups into the green-sand. We 

 are not to conclude from these facts that certain sets of fossils may 

 not serve as good chronological tests of geological periods, but we 

 must be cautious not to attach too much importance to particular 

 species, some of which may have a wider, others a more limited 

 vertical range. The phsenomena alluded to are strictly analogous 

 to those with which we are familiar in the more modern deposits, 

 where different tertiary formations contain some peculiar Testacea, 

 together with others common to older or newer groups, or whei'e 

 shells of species now living in the sea are associated with others that 

 are extinct. 



An assemblage of fossil shells has been presented to our museum 

 by Mr. J. Leigh and Mr. J. W. Binney, found at Collyhurst near 

 Manchester, in red and variegated marls, which were I'eferred by 

 them at first to the upper division of the new red sandstone group; 

 but Professors Sedgwick and Phillips consider them to be a red and 

 variegated deposit, belonging to the magnesian limestone series. 

 As these fossils are new and characteristic of a particular subdivi- 

 sion of the beds between the lias and coal, it is to be hoped that 

 they will soon be described and figured. 



The petrifaction of wood, and more especially its silicification, 

 still continues to present obscure problems to the botanist and 

 chemist. The first step towards their solution will probably be 

 made by carefully examining vegetables in different stages of petri- 

 faction ; and with this view Mr. Stokes has procured several speci- 

 mens of wood, partly mineralized and partly not. Among these is 

 a piece found in an ancient Roman aqueduct in Westphalia, in 

 which some portions are converted into spindle-shaped bodies 

 consisting of carbonate of lime : while the rest of the wood 

 remains in a comparatively unchanged state. The same author 

 has pointed out cases both of siliceous and calcareous fossils. 



