1 58 Chemical and Geological Essays of T. Sterry Hunt. 



Greenough, in his anniversary address to the Society, on the 21st day 

 of Febrnary, 1834, said: 



Mr. Murchison has employed three summers in examining a range 

 of country situate between Shrewsbury and Cserniarthen ; and the 

 geological positions, as well as the mineral and zoological characters of 

 the several rocks which border England and Wales, are now determined 

 with as much exactness as those of any portion of the secondary 

 'system. Taking the old red sandstone as aline 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 limestone of 

 Amestry and Ledgley ; 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 1,000 feet. 



2. The Dudley or Wenlock series consisting of limestone ; its thickness 

 may be taken at 2,000 feet. 



3. The Horderly or May Hill series, composed of party-colored sand- 

 stone, conglomerate and impure calcareous flagstone; it is said to 

 attain a thickness of 2,500 feet. 



4. The Builth or Llandeilo series, a black flagstone, characterized by 

 the Asiiphus Buchi'i. 



5. The Longraynd or Linley series, consisting of coarse roof slates, 

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



It is well known that Prof. Sedgwick has studied with equal assidu- 

 ity 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. Mur- 

 chison are for the most part exceedingly well characterized by their 

 fossil contents. Some of the shells which he has discovered 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 Scotland, Ireland, Germany, 

 Russia, Sweden and North America, has hitherto presented to the 

 observer a mere scene of confusion." 



On the 19th day of February, 1836, Mr. Charles Lyell, President 

 of the same society, in his anniversary address, said : 



"It is with pleasure that I next call your attention to the investiga- 

 tions whiidi Mr. Murchison has boen steadily pursuing in the older 



