Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/493



PLATE 11.

This plate represents a fragment of the rock of Kinnoul, including the junction of the schist and the trap. The vesicular cavities are seen running in lines parallel to the laminæ of the schist, and increasing in size and number where they approach to the trap. The contortion of the laminæ is also represented at the points where the two rocks unite, and in the same place the appearance of a detached fragment is visible. There is unquestionable proof of the existence of such detached fragments in many cases, as they may be found entirely surrounded by the trap, and only discoverable after breaking it. The conversion and prolongation of the schist into ramifying veins is also shown, the schistose structure disappearing shortly after the change takes place.

PLATE 12.

Forms of crystals to illustrate Mr. Phillips's paper on the Measurement of Primitive Crystals by the reflecting goniometer.

PLATE 13.

Map and Sections of the Plastic Clay District on the south-east of London.

The colours represent, 1. Chalk. 2. The formation of Plastic clay. 3. That of the London clay. 4. The tract of Marshes lying along the banks of the Thames—the flat grounds of Southwark, St. George's fields, Battersea and Chelsea, are coloured as belonging to this district, since they appear to hate remained in the state of unreclaimed marshes even within the period of historical record: beneath a great part of this district lie the remains of an extensive forest, (vide page 304).

The numbers marked upon the map denote various points, where either natural sections are exhibited or where pits have been opened.

1. Marks the section ascertained by Sir Christopher Wren while laying the foundations of the new Cathedral of St. Paul; see Parentalia and page 287 of this volume.

2. The Tunnel at Rotherhithe or Redriffe; see the section as given in Mr. Webster's paper on the Strata lying over the Chalk, Geol. Trans. vol. ii. page 197. It should be observed that the section of the southern shaft only is there given. In the northern a thickness of nearly forty feet of the London clay was exhibited, in consequence of the dip of the strata in that direction.

3. Between Camberwell and Peckham. Here the shelly beds of the Plastic clay have been found in digging wells at the depth of thirty feet. At New Cross, near this point, they are found at the surface.