450 Geological Society. 



After careful examination of the Old red Sandstone, Mr. Murchi- 

 son has proposed to divide it into three parts : the uppermost, cha- 

 racterized by quartzose Conglomerate ; the middle, by Cornstone ; 

 the lowermost, by Flagstone. The cornstone and marlstone of the 

 middle group contain undescribed genera of Crustacea ; and in the 

 tilestone beneath are found some defences of fish, together with a 

 few remains of testacea. 



Mr. Murchison has employed three summers in examining a range 

 of country situate between Shrewsbury and Caermarthen; and the 

 geological positions as well as the mineral and zoological characters 

 of the several rocks which border England and Wales are now deter- 

 mined with as much exactness as those of any portion of the secon- 

 dary system. Taking the old red sandstone as a line of departure, 

 the rocks beneath are disposed in descending order as follows: 



1. The Ludlow series, divisible into three parts, the upper, 

 middle and lower. To the middle belong the well-known limestones 

 of Amestry and Sedgley : the upper and lower consist of sand, marl, 

 or flagstone, having some fossils peculiar to each, and others in 

 common. The thickness of the whole is estimated at 1000 feet. 



2. The Dudley or Wenlock series, consisting of limestone : its 

 thickness may be taken at 2000 feet. 



3. The Hordesley or May Hill series, composed of party-coloured 

 sandstone, conglomerate and impure calcareous flagstone : it is said 

 to attain a thickness of 2500 feet. 



4. The Built or Llandilo series, a black flagstone, characterized 

 by the Asaphus Buchii. 



5. The Longmynd or Linley series, consisting of coarse roof slate, 

 sandstone and conglomerate ; no fossils have been discovered in it. 



It is well known ihat Professor Sedgwick has studied with equal 

 assiduity the rocks which lie beneath those I have mentioned. 

 When his observations are published, the Society will have a type 

 of the whole of the transition rocks of Wales. The rocks described 

 by Mr. Murchison are, for the most part, exceedingly well charac- 

 terized by their fossil contents. Some of the shells which he has dis- 

 covered, appear to have escaped the notice of antecedent observers; 

 but the genera, if not the species, of others, may occasionally be found 

 in the works of Hisinger and other continental writers. If, then, the 

 transition as well as the secondary and tertiary beds can be identified 

 over great tracts of country by their fossil remains, let us hope that 

 a clue is now at hand, by which we may find our way through that 

 vast assemblage of beds, which, not in England only, but in Scot- 

 land, Ireland, Germany, Russia, Sweden, and North America, has 

 hitherto presented to the observer a mere scene of confusion. 



In Mr. Murchison's paper we find also, traced with exactness, se- 

 veral hitherto unexplored lines of disturbance, producing sometimes, 

 as in the Abberley Hills, a complete inversion of dip. The rocks 

 which border the old red sandstone, acquire in some places an 

 anticlinal dip, and reappear in parallel ridges far westward of their 

 natural site, insomuch that the Ludlow series is met with even in 

 Montgomeryshire. Mr. Murchison has examined in detail the trap- 



