Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/336

 parallelism in the horizontal one, and causes, as will be readily comprehended, the distance between any two approximate ones to vary exceedingly, a circumstance of importance in examining some of the speculations which have been formed relating to their cause and origin. In these circumstances it would be as useless as it would be difficult, to give the measures of their variations. It is sufficient to remark that the nearest horizontal distance between the uppermost and nearest lines may be taken at 150 or 160 feet, and the greatest between the two lowermost and most distant ones at 1000; an approximation sufficiently accurate for the purpose. But the vertical distances as ascertained by the spirit level are 82 feet between the uppermost and second, and 212 between the second and lowermost. I have omitted fractions in this measurement, because the irregularity of the ground is such, and the uncertainty of the true surface of the line so great, that it is impossible to determine this point to a great nicety. The slope of each line is likewise so considerable, and at the same time so various, that a great variation of this vertical distance would take place according to the point adopted as the station of the spirit level, and I have therefore fixed it at the middle of each line. I need not here call the reader's attention to the distances between the uppermost line and the top and bottom of the glen respectively, as these will fall more properly to be considered when the general levels of the surrounding vallies and outlets are examined. For the same reasons the aspect and materials of the lines themselves will be best considered when I have described the mineralogical structure of the whole glen, and particularly that of the surfaces on which they are formed.