231 



continued exertions to investigate both the physical condition 

 ind history of the species; and again, I know of no series of 

 etermine to us the secular movements, or gradual oscillations 



relatively the water-, than these transitional accumulations 

 L- post-Triassic or pre-Liassic age. 

 ) of rocks, and section at Westbury, help us by their 



position, as well as geological horizon, to examine and 

 he conditions of the Keuper Marls at their close, and the 

 id allied Rhsetic series upon them, and also the base of 

 IS, as evidenced by the Planorbis Zone at the summit of the 



in position, at its junction with the Transitional or Ehsetic 



one of tlie few places where evidence is clearly afforded 

 lide us to a right understanding of the many fluctuations and 

 iformities, arising from slow oscillation of the land, 

 1 of organic and inorganic matter, and the corresponding 

 of life in an estuarine, or shallow sea. For I cannot 

 , the Rhsetic series coiild have accumulated, or have 

 I imder any other conditions, than on a slowly-descending sea 

 ited pauses (as evidenced by the numerous Bone beds and 

 le bands), extending over great intervals of time, which thus 

 steadily produced the alternating conditions so manifest in 

 5tructure of the shales, mai'ls, and thin limestones of the 

 ng the structure of tlds section in particular and others 



DISTRIBUTION. 



and to some apjiarently insignificant section on the banks 

 , at Westbury, as well as two or three others which occur 

 cent valley watered by this grand river, are English tyi)es 

 ively developed rock.s of the same age and physical aspect 

 lombardy, France, Hanover, Savoy, Saxony, Bavaria, and 

 c. ; and although with us the series is never found to exceed 

 eet in thickness, including (according to our new reading) 

 sn, and white marls of the Upper Trias, yet the fact of 

 eloped Palffiontological featui*es agreeing in almost every 

 cter with the Continental deposits, enables us to co-ordinate 

 tuna, the entire series in this countiy with those of Europe 



mplete series exhibiting all these groups in succession is seen near 

 3 every bed, from the Tea green Marls of the Upper Trias, to the 

 is measurable in one cliflF section. 



