Geological Society. 403 



the species found in the Silurian system, but resembling those ob- 

 tained in the mountain limestone. The same group contains also 

 new species of Trilobites and Crinoidea. 



In the next underlying formation in the north, or the sandstone 

 group, ranging from Baggy Point by Marwood and Sloly, occur new 

 species of Oucullcea, Avicula ? Cypricardia, and Orthocera ; one cast 

 also has been obtained, undistinguishable from Bellerophon globatus 

 of the Silurian system. In the same series are found casts of plants 

 of considerable size, but in Professor Henslow's opinion, quite 

 distinct from any known coal measures remains. 



In the third descending group, but few fossils have yet been 

 found, yet it has been ascertained to contain one of the varieties of 

 Producta common in the overlying groups, and similar to the spi- 

 nous species of the mountain limestone ; also a coral (Favosites po- 

 lymorpha,) previously found in England only in the Upper Silurian 

 rocks. 



The next descending series of beds, or the arenaceous deposits of 

 Linton, contains few fossils, except towards its lower part, where 

 calcareous matter re-appears, and in that portion a Spirifer has been 

 obtained resembling the S. attenuatus of the mountain limestone, 

 and a new species of Orthis, a genus characteristic of the Silurian 

 system. 



In the Quantocks, which the authors consider as formed of the 

 oldest strata in North Devon, organic remains appear to be rare, the 

 principal hitherto procured consisting of Favosites polymorpha. 



South Devon. — Having thus shown that in North Devon there is 

 a regular succession of strata characterized by distinct fossils differ- 

 ing more and more in descending order from the organic remains of 

 the mountain limestone, and approaching those of the Silurian sy- 

 stem ; the authors proceed to enumerate the order of the groups and 

 the imbedded fossils in South Devon and the North of Cornwall. 

 They show a similarity of succession of deposits and of organic 

 remains in the upper groups, but they state that in consequence of 

 the protrusion of the granite, there is in the lower a considerable 

 difference in mineral type, especially south of Dartmoor. They 

 refer, however, to their former memoir for ample details respecting 

 these counties, and for proofs that they were correct in placing the 

 great calcareous masses of Plymouth and Chudleigh on the same 

 parallel as the lowest calcareous strata of North Devon. 



In conclusion, the authors show, that the variation in Devon- 

 shire and Cornwall from the ordinary type of the old red sandstone 

 in Herefordshire and adjoining counties, cannot be admitted as a 

 valid argument against assigning the slates and sandstones of these 

 counties to that system, because the variations in composition of 

 other formations within limited areas is equally great. They show 

 also that the absence of the true carboniferous limestone in Devon- 

 shire cannot disprove their present classification, because in Western 

 Pembrokeshire that limestone is wanting, and the coal measures 

 rest on older formations. 



In consequence of mineral character being no longer indicative 



2D2 



