742 REPORT — 1900, 



stream as suggested by Mr. Marr. The coal seam mentioned is well known to me. 

 On searching it I found several Product! fairly perfect embedded in it and filled 

 with it, and the conclusion I came to was that it was either a coal-seam which had 

 grown on a reef and been submerged, or a deposit of seaweed. These Producti 

 seem to disagree with the injection theory. Such coal-seams are found occasionally 

 in the limestone. One near Kirkby Lonsdale has been worked for coal. 



Mr. MaiT has mentioned two places where knolls of grit occur. I do not admit 

 that a knoll of grit can have anything in common with the reef knolls of Craven 

 unless it be the external form ; but if such structures were made by earth thrusts 

 and abounded, it would no doubt be a strong point in favour of his views. One of 

 these grit knolls is said to be in the canal at the back of Sliipton Castle. I think 

 this must be an error. I know of no sandstone in that locality, though I know it 

 well. I have consulted others who are, as geologists conversant with Shipton, 

 competent to form an opinion, and they agree with me that nothing but limestone 

 and shales occurs in that canal at that point. The beds there are certainly con- 

 torted, but not sandstone, and contortions do not necessarily imply reef-knolls. 



I feel unable to regard Mr. Marr's ' model knoll ' as in any respect resembling 

 what I have called reef-knolls. That is, according to his views, a broken plication 

 of a thin hard bed of limestone in a mass of softer shale, the ."hale surrounding its 

 broken fragments. The knolls to which I allude are almost solid limestone from 

 top to ba.se. They have no alternations of hard and soft beds, and, so far as I have 

 seen, no repetition of beds by folding. The evidences of movement on their flanks, 

 if any, are not more than one would expect from the vertical pressure of a more or 

 less plastic shale upon what is at least a less plastic limestone. 



1 admit fully that there are abundant evidences in the district of faulting, of 

 great pressure, and quite likely of over-thrusts ; but to say that these have given to 

 these rocks a change of character, or are responsible for the order of their succes- 

 sion, appears to me to be invoking an unnecessarily powerful but yet inadequate 

 force. Such thrust-planes as are implied would meet the geologist in the field at 

 every turn, and force themselves into recognition. Tliey would admit of easy 

 mapping, and no statement of their existence can be complete without some such 

 systematic recognition. 



3. On the Construction and Uses of Strike Maps. 

 By J. LoMAs, A.R.C.S., F.G.S. 



In studying the deformations which a series of rocks have undergone, we are 

 apt to regard the vertical movements as all-important, and neglect the horizontal 

 movements to which they have been subjected. This is largely owing to the 

 difficulties experienced in picturing such horizontal movements and representing 

 them on a plan. 



Lines dependent on surface inequalities confuse the worker when he seeks to 

 use the ordinary geological maps for this purpose. 



It is easy to get rid of these lines by projecting the strikes of the beds on to a 

 horizontal plane. We then have the appearance that would be produced if the 

 country were planed down to a horizontal surface. The outcrops would coincide 

 with the strikes, and any deviation from straight lines would indicate horizontal 

 movements. 



Vertical movements would also be shown on such a plan by the closing up of 

 outcrops of beds of equal thickness. 



All the necessary data necessary to represent these features on a strike map 

 are given in the ordinary Geological Survey Sheets. 



To construct such a map, first trace the dips given on the geological map and 

 draw short lines at the points of the arrows, at right angles to the direction of dip. 



We thus have represented the strikes of the beds at a number of points. Now 

 it is necessary to connect these up by lines to show the strike at intermediate 

 places. 



It would not be safe to connect one line with another, as the strikes may refer 

 to difierent beds. 



