153 



the adjacent counties we are indebted to Mr. Murchison. The fol- 

 lowing are the conclusions which his paper tends to establish. 



1. In the Shrewsbury coal-field the presence of a younger se- 

 ries of coal-measure than has hitherto been noticed^ characterized 

 by the freshwater limestone above alluded to. 



2. The recurrence of these beds at Coalbrook Dale, over an older 

 series of coal-measures which at one spot repose on mountain lime- 

 stone, at other places either on the old red sandstone or on transi- 

 tion rocks. 



3. The absence of these upper beds at the Titterston Clee hills, 

 where the lower beds rest in two places on mountain limestone, but 

 generally on old red sandstone, as they do invariably on the brown 

 Clee hill, in the forest of Wyre and at Newent. 



4. In some of the poor and ill-consolidated coal-beds, particularly 

 in the upper part of the series, the characters of the fossil plants, both 

 generic and specific, can be recognised in the coal itself. 



5. The mountain limestone where it does occur in this part of the 

 country is of inconsiderable thickness, and wedge-shaped, so that it 

 shortly disappears entirely. Its absence, therefore, is not to be im- 

 puted to mighty convulsions, but to partial and scanty deposition in 

 the first instance. 



At Shaftoe, near Wallington, in Northumberland, Mr.Trevelyan* 

 has observed among the constituents of the millstone grit, the low- 

 est bed of the regular coal-measures, transparent fragments of gar- 

 net ; they occur there rather abundantly. He has also remarked 

 in other northern coal-fields small portions of hornblende in a simi- 

 lar situation. 



The Rev. Mr. Williamson has directed attention to certain ra- 

 vines in the Mendip hills, and other heights which bound the coal- 

 field of Bristol. These ravines cross the ridges transversely so as 

 to connect the opposite valleys, being occupied in part by horizon- 

 tal beds of dolomitic conglomerate and lias ; he infers that the frac- 

 tures took place before these rocks were deposited, and that the 

 bone-caves were formed at the same period. 



Dr. Lloyd first observed fossil fishes in the old red sandstone. Mr. 

 Murchison finds the observation true over a considerable extent of 

 country J they belong chiefly to the genus Cephalaspis of Agassiz j 

 they have also been described by Dr. Fleming, as having been met 

 with in the old red sandstone of Forfarshire. They appear not to be 

 diffused through the formation generally, but to be confined to the 

 middle portion of it, the cornstone. 



The nature of the pebbles imbedded in the Old Red Conglomerate 

 varies according to its locality. In Scotland they are very fre- 

 quently of gneiss, as is the case in the neighbourhood of Baden- 

 Baden. 



In an Account of the Trap Rocks of the Border Counties, and 

 their effects on the Stratified Beds with which they are in contact, 

 Mr. Murchison has separated the objects of his examination into three 



* Lond. and Edinb. Phil. Mag. and Journ. of Science, vol. vi. p. 76, (1835.) 



