Page:Quarterly Journal of the Geological Society of London, vol. 31.djvu/83

Rh IN THE ISLE 0E PORTLAND AND AROUND WEYMOUTH. 37 Cyrene media. Physa Bristovii. Hjdrobia. Planorbis. Cypris striato-punctata. legumen or fasciculata. This mass of debris is angular or subangular, and is little or not at all worn— weathered only. It is not stratified, but roughly spread out with thin intercalated irregular seams of the same loam as d'. The loam itself shows traces of rough stratification, and con- tains thin lenticular seams of the angular debris, indicating the one and the other to be phases of the same phenomenon. Near where the loam and rubble thin out is another feature which deserves notice. The old beach is here a loose shingle, and has been worked and removed over a considerable extent. This cleared area presents, however, a series of low ridges or walls, running nearly north and south, which have been left by the workmen. On exami- nation these are found to consist of the loam and rubble beds, d' and Fig. 5. — Section showing the longitudinal breaks caused in the old beach by fissures filled by land-materials from above, but open ■ Shingle-pit, between section 4 and the landmark. d d' e Base of pit 12 is o «H tc ^ _ I © u 1. Purbeck beds. 2. Portland rock. d. Soil and dark loam, with angular fragments. d Loam, laminated, e. Raised beach. /. Open fissures. d, which have replaced the shingle. The cause of this is not difficult to find. On prolonging these loam-ridges to the edge of the cliff further southward, I invariably found them to correspond with one of the many lines of fissuref by which the island is traversed from be referred to Nos. 57, 70, 77, and 82 of his section of Ridgeway (see Damon's Geol. of Weymouth, p. 107). f These fissures follow the lines of joint, which run within a few degrees on either side of N. and S., and, with the same variation, E. and W. A N.-and-S. fissure will sometimes pass into oneE. and W., and afterwards resume its first direction. They are not caused by an outward, or seaward, slip over the Kimmeridge Clay ; for the beds dip slightly inwards, or inland, forming a shallow synclinal running vN". and S. along the centre of the island. In the above section (fig. 5) the lower part of the debris above / is represented too fine : it consists of large and small angular blocks of Purbeck and Portland beds.