THE CAMBRIDGE GAULT AND GREENLAND. 315 



the Vertebrate fossils were often contained in hollows of the surface 

 of the Gault. Occasionally the phosphatic bed was covered by a 

 discontinuous dark-coloured clayey bed, divided from the Chalk Marl 

 by a sharp line of bedding. He thought that this band might result 

 from denudation of Gault ; and the fact that it did not interfere with 

 the continuity of the bed of phosphatic nodules seemed to show that 

 the denudation was local and of small extent. The fact that sand 

 was superimposed upon clay, necessarily implied an upheaval of the 

 sea-bottom ; and therefore the newest-formed beds of the Gault were 

 sure to be denuded to some extent in consequence. But while this 

 circumstance would explain the occurrence of a small percentage of 

 Gault species, it rendered it rather improbable that so varied a 

 fauna should have been derived from a denuded portion of one 

 stratum. Mr. Seeley's own investigations had not led him to detect 

 in the bed any preponderance of Gault forms. He further found 

 that the remains of Yertebrates in the Cambridge Upper Greensand 

 were associated series of bones, which would not be the case were 

 they derived fossils, and that no species of reptile had yet been 

 identified as common to the Cambridge Greensand and the Gault. 

 He thought that the thinness of the Cambridge Greensand, as well 

 as the complex nature of its fauna, was only to be understood by 

 considering the circumstances of physical geography under which 

 the deposit originated ; and upon this some light was thrown by the 

 thinness of the Kimmeridge Clay in the same area, and by the oc- 

 currence of phosphatic nodules in that area in the so-called Neo- 

 comian beds. These beds, like the Cambridge Greensand, contain 

 fossils derived from the Carboniferous Limestone and fragments of 

 Palaeozoic rocks ; so that the phosphates might have been furnished 

 to the sea in which the deposit was formed by denudation of erup- 

 tive dykes of apatite, such as Mr. D. Forbes had informed him were 

 to be met with traversing Palaeozoic rocks in Spain, Norway, and 

 other countries. Taking all these facts into consideration, he was 

 inclined to hesitate for the present in accepting Mr. Jukes-Browne's 

 hypothesis. 



Mr. Forbes, with reference to Mr. Seeley's observations, stated 

 that he had found true eruptive lodes or dykes of phosphate of lime 

 (phosphorite or apatite) traversing the Silurian and Devonian strata 

 and granites of Estremadura in Spain and Portugal, and often ex- 

 tending for miles, and also others breaking through the metamor- 

 phic schists of the south of Norway. Some years back he had ex- 

 plained the phosphorite in the deposits of Nassau as resulting from 

 submarine eruptions, which brought it up and left it on the sea- 

 bottom in the form of breccia and tuff, precisely as a volcanic rock 

 would do under similar circumstances. So far as he had examined 

 the phosphatic nodules of the Cambridge Greensand, however, he had 

 not found that their mineral structure indicated any such eruptive 

 origin. 



The Bev. T. G. Bonkey remarked that Mr. Seeley's observations 

 bore upon a large question, affecting our whole system of geological 

 nomenclature rather than the immediate subject. The nomenclature 

 being as it was, he thought Mr. Browne was fully justified in his con- 



