SUPPLEMENTARY NOTE C. 121 



suspended and in a chemically dissolved state ; so that, while 

 the latter may be carried out into the open sea, to be appro- 

 priated by shells, corals, &c. for their skeletons, and the debris 

 of these converted into limestones, the former may be mechani- 

 cally deposited in estuaries and along shores. I have often 

 thought over the fact that many limestones are so greatly 

 deficient of calcareous fossils as to render their organic origin 

 doubtful : the lithographic limestones of Bavaria are cases in 

 point, also the Permian marl-slates of Durham and Germany. 

 I am therefore now strongly inclined to assume that these and 

 other calcareous deposits are of mechanical origin. 



When writing the footnote above referred to, I thought it not 

 improbable that the dolomitic -conglomerate of the Bristol 

 district was a Triassic glacial deposit, its paste having been 

 derived from a Permian magnesian limestone now entirely 

 removed. But from information I have liberally received from 

 Prof. Sollas (whose short note in the f Geological Magazine ' of 

 February last led me to put a few questions to him) I feel per- 

 suaded his opinion is correct, that both the paste and the pebbles 

 it contains have been dolomitized since they were accumulated, 

 and that the paste had not been derived from a Permian 

 limestone. Prof. Sollas and Mr. Margetson, I understand, are 

 preparing for publication an account of the Bristol rocks. 



