A. B. Wynne— The Salt Mange. 411 



miles, and shearing, so largely affecting Mr. Middlemiss's views, 

 and which arm his criticisms, were in their early infancy or still 

 unborn, and had not been developed by the exhaustive researches 

 in complicated districts of the Scottish geologists, whilst complex 

 superficial displacements from landslip abounded in degree and 

 magnitude sufficient to render conclusions as to inversions, etc., such 

 as the paper advances, very doubtful. 



One conclusion (not the author's alone), namely, that the Boulder 

 beds form a single continuous horizon, seems incontrovertible upon 

 the accepted evidence advanced for unconformity. This relation is 

 easier to understand when it is assumed that the Salt Marl is an 

 accidental associate, and not integral as an original basal part of the 

 series. Kegarded as of the latter nature, in intimate connexion 

 with the lowest succeeding members, whether boulder conglomerates 

 or sandstone, it was of course impossible to hold such boulder 

 rocks to be contemporaneous with others, at a higher stratigraphical 

 level, in an apparently perfectly conformable sequence. The inter- 

 pretation depended upon the existence of either conformity or 

 discordance within beds lying in a general way more or less 

 horizontally, and the question formed one of those problems more 

 likely to be solved by the application of broad considerations than 

 of local details. 



The paper itself suggests an illustration of this where reference 

 is made to derived pebbles as proofs of discordance ; for it is an 

 uncontested fact that sandstone beds in the Eocene group trans- 

 Indus enclose rounded pebbles of fossiliferous Nummulitic limestone, 

 and are overlaid by conformable beds of similarly fossiliferous 

 Eocene limestone with little or no disturbance (Mem. G. S. I. vol. xi. 

 p. 3o,et.s.). In other cases formations containing rolled fragments 

 of their own rocks have also been recorded. The inference from 

 these cases is quite as strongly in favour of conformity as of dis- 

 cordance : in fact, as strict evidence of the latter, the occurrence of 

 these pebbles has little or no weight. If this be true of trans- 

 Indus Nummulitic pebbles, why should it be otherwise as to 

 dolomite pebbles from the Salt Marl in an overlying conglomerate ? 

 or as to Eocene limestone pebbles in the next Tertiary layers above ? 

 In each case the separation as to time is reduced, and the likelihood 

 of a break diminished, leaving to wider general considerations rather 

 than to dogmatic rules the position of the safest guides. At the 

 same time the contention of Mr. Middlemiss may be correct, but 

 the case affords an instance in which each observer is at liberty to 

 form, or even to alter, his own conclusions according to his lights. 



The most important part of the paper is the author's suggestion 

 that the sub-Cambrian Salt Marl has no ordinary stratigraphic 

 relations with the rest of the series, but is of plutonic, igneous or 

 deep-seated origin, introduced in Tertiary times, accompanied by 

 lateral and vertical disturbance, thrusting, and shearing. The idea 

 of an igneous or deep-seated origin for rock-salt formations is not 

 new ; it was considered and discussed so far as possible before 

 my Salt Eange Memoir was written, but there did not then seem 



