1950 article said that the drainage through the oolite was so good that construction was probably started from the foot of each shaft without drainage. Brunel was quoted as reporting in October 1841 that, "the drainage of the water is obtained into the lower oolite, without pumping, at one of the intermediate shafts" Therefore, although it included the geological cross-section (drawn by GWR engineer, Mr. R. P. Brereton), it made no mention of fuller's earth problems. Later articles say the section shows that the header, on the originally-proposed deeper level, passes through a much greater length of fuller's earth than the tunnel as built, and that it also makes it clear that information gained from digging the shafts would have made it apparent that this would be the case. This diagram also casts doubt on the unsupported assertions which are sometimes made that the gap between the two tunnels is the result of a roof collapse in the early days of the tunnel. This gap coincides precisely with the level section at the summit of the line, and also with a dip in the contours of the ground above which brings the ground level below the depth at which the transition from tunnel to cutting is made at the outer ends of the tunnels. It is unlikely that a chance collapse would have taken place to correspond with these features with such convenient precision. The gap is also shown to be in the more stable oolitic strata rather than the unstable stretches of fuller's earth which are more liable to collapse. The lateral alignment of the revised tunnel route was the same as the planned deeper route, and this left the ten exploratory shafts intersecting the tunnel and continuing as pits up to 6 metres deep below the tunnel floor. The pits were capped with timber to support the track and ballast. However, no records were left as to whether or not the pits had been filled in. In 1950 a train driver noticed a void beneath the tracks and it became apparent that work was required to stabilise the pits. The original timbers were removed and the pits spanned with prefabricated concrete beams reinforced with bullhead rail and shear links. One more beam was fabricated than was required for the work and this was stored in a nearby yard. Again it was not recorded whether the pits were filled.