493 



shales at Bideford were interstratified with rocks charged with 

 shells or other fossils known to belong to rocks older than the old 

 red sandstone. 



Since writing the above sketch of the different views recently 

 published of the structure of Devonshire, I have received a letter 

 from Mr. De la Beche, from which I am happy to learn, that it is 

 his intention before concluding his report on the Ordnance Map 

 of Devon, to reexamine Devonshire. He is far, he says, from 

 pretending that his first views were perfect, and if he finds rea- 

 son to modify any of them, he shall not hesitate to announce the 

 change of opinion. In the mean time he no longer contends that 

 the culmiferous strata are referable to the lower greywacke, and 

 considers the point of difference to lie witliin a narrower compass, 

 namely, whether the culm beds are to be considered as upper grey- 

 wacke or coal. This question, on which he is not yet satisfied, evi- 

 dently appears to him of much less theoretical importance than, I 

 confess, it does to me. It is fair, however, that I should state the 

 arguments which influence his mind. If the plants, he says, found 

 at Bideford in the culmiferous series should belong to strata more 

 ancient than the old red sandstone the fact would not stand alone, 

 for he has lately received a letter from M. Elie de Beaumont, de- 

 tailing analogous phsenomena in Brittany. It is stated that the grey- 

 wacke there closely corresponds in general character with that of 

 Devon, the upper part like the Devonian series containing anthra- 

 cite. With this anthracite or culm are found at Montrelais, Chatelai- 

 son, and other places, fossil plants, the greater part of which are 

 identical with those in the coal measures ; but there are others which 

 have not hitherto been detected in the latter rock. Patches of true 

 coal measures rest in unconformable position upon these upper 

 greywacke beds of Brittany. Now I regret that I have not seen 

 any printed account of the geology of this part of France ; for until 

 we learn whether the plants in question are associated with true Si- 

 lurian fossils, the testimony is quite incomplete. We know not, 

 for instance, whether the plant-bearing series in question is old red 

 sandstone or a Silurian formation, or whether it is a lower part of 

 the true carboniferous system of which the strata had been disturbed 

 before a higher portion was superimposed. 



Similar remarks hold in regard to the observations made by 



2n 2 



