Correfipondencc — C. N. Bromehcad. 141 



SOLUTION TIIEOllY OF VALLEY FORMATIOX. 



Sir, — In the December number of the Geological Magazine there 

 appeared a short article by Mr. Jukes-Browne on the subject of the 

 solution theory of valley formation as applied by the Rev. E. C. Spicer 

 to the area of the Glyme and Dome. It seems to me that there are 

 several points in this paper that demand some attention. 



It is said that Mr. Spicer's proposition "assumes that the rocks of 

 the district are traversed by a double set of joints which coincide 

 approximately with the winding of the streams, but no evidence is 

 adduced to prove that this is actually the case, and his own map 

 shows that the windings of the Glyme and Evenlode are so irregular 

 that they cannot be reduced to the intersection of two sets of lines. 

 This map is reproduced, so that the reader can judge for himself". 

 I have studied the map in question, and also traversed the ground 

 several times, twice under the guidance of Mr. Spicer. Though the 

 map was not drawn with that intention, it seems to me to show very 

 clearly the tendency of the Evenlode, Dome, and Glyme to twist in 

 right angles, and so indicate a set of lines which may well coincide 

 with joints. It is a very suggestive fact that where the Evenlode 

 runs across the Lias this tendency appears to vanish. 



No one who looked at the question impartially would expect to 

 find a network of joints accurately indicated by valleys in such an 

 ' advanced ' stage as those of the Evenlode, Dome, or Glyme. The 

 right angles are practically gone from the Cher well Valley, but are 

 very characteristic of many of the valleys in the area under discussion 

 which are still dry, and are shown by such ' embryo ' solution valleys 

 as may be seen near Wooton and (outside the area) at Cuddesdon. 



A little further on we read that "on this [Mr. Jukes-Browne's] 

 view it is easy to understand why there is only one valley system, but 

 if Mr. Spicer's theory were correct we ought to find traces of an 

 ancient system of mechanically formed valleys which did not coincide 

 with the subsequently formed ' solution valleys ' ". We do find traces 

 of such a sj^stem. The most noticeable instance is described by 

 Mr. Pocock in the Geological Survey Memoir on the country round 

 Oxford, under the name of the ' Wilcote Valley' (p. 92). While the 

 covering of Oxford Clay was still nearly continuous over the area, the 

 AVindrush joined the Evenlode near Ashford Mill, a fact which is of 

 great importance in considering the ' misfit ' of the Evenlode. As the 

 clay was removed a solution valley was developed which finally broke 

 into the Windrush Valley and led it into the present course past 

 Witney. But the pre-solution mechanically formed valley between 

 Wilcote and Northleigh remains, flanked on the south by the outliers 

 of Oxford Clay alluded to by Mr. Jukes-Browne. 



The part played by landslips in the formation of valleys has 

 certainly received little attention. That many of the chalk valleys 

 are frequently widened by small slips no one who knows them will 

 deny ; it is possible, too, that slips may occasionally serve to lengthen 

 such valleys, but for obvious reasons they can neither initiate nor 

 deepen them. 



