380 CAMBRIAN AND SILURIAN IN EUROPE. [XV. 



which excluded the passage-beds, and caused the Lower Silu- 

 rian to rest unconformably upon the Longmynd rocks. (Ibid., 

 256 ; and Plate 31, sections 3 and 6 ; Plate 32, section 4.) But 

 in Siluria (1st ed. 47) the two are stated to be conformable ; 

 and in the subsequent sections of this region, made by Aveline, 

 and published by the Geological Survey, the evidences of this 

 want of conformity do not appear. Murchison at that time 

 confounded the rocks of the Longmynd with the Cambrian 

 (Bala) beds of Caermarthenshire and Brecon. (Silurian Sys- 

 tem, 416.) Hence it was that he gave the name of Cambrian 

 to the former ; and this mistake, moreover, led him to place 

 the Cambrian of Caermarthenshire beneath the Llandeilo. It 

 is clear that if he claimed no well-defined base to the Llandeilo 

 rocks in this latter (their typical region), it was because he saw 

 them passing into the overlying Bala beds. There was, in the 

 error by which he placed below the Llandeilo, strata which 

 were really above them, no ground whatever for afterwards 

 including in his Silurian System, as a downward continuation 

 of the Llandeilo rocks (which are the basal portion of the Bala 

 group), the whole Festiniog group of Sedgwick ; whose infra- 

 position to the Bala had been shown by the latter long before 

 it was known to be fossiliferous. 



It was, however, claimed by Murchison that no line of sepa- 

 ration can be drawn between these two groups. The results of 

 Bamsay and of Salter, as set forth in the address of the former 

 before the Geological Society of 1863, and more fully in the 

 Memoirs of the Geological Survey (Vol. III. Part II.) published 

 in 1866, with a preface by himself, as the director of the Sur- 

 vey, are completely ignored by Murchison. The reader famil- 

 iar with these results, of which we have given a summary, 

 finds with surprise that in the last edition of Siluria, that of 

 1867, they are noticed in part, but only to be repudiated. In 

 the five pages of text which are there given to this great Mid- 

 dle Cambrian division, we are told that the distinction between 

 the Lower Tremadoc and the Lingula flags " is difficult to be 

 drawn," and that the Upper Tremadoc slate passes into and 

 forms the lower part of the Llandeilo (under which name 



