AND PRESERVING FOSSILS. 135 



colour-streaks, and fossils must be looked for on planes parallel 

 with the latter. 



Such slaty rocks, though apparently barren, may prove (like the 

 Welsh Cambrian rocks) to be very fossiliferous, if the organic 

 remains are sought for on the edges of slabs, sometimes at light 

 angles to tlie cleavage planes. 



2. In compact limestones fossils are often difficult to discover, 

 except on weathered surfaces. The old faces of quarries, exposed 

 natural sections, and stone walls should therefore be examined with 

 care. 



Even when limestones appear to be unfossiliferous, it is well 

 to examine them — and especially the cherty bands and nodules so 

 frequent in them — with a good hand-lens to detect microscopic 

 organisms. Shells of Eoraminifera and Radiolaria, spicules of 

 Sponges, etc., may frequently be detected by a lens on smooth, 

 wetted surfaces. 



3. Similarly, apparently unfossiliferous clays are not to be 

 neglected. Samples may be taken and " washed " at home, the 

 result being frequently abundant remains of Eoraminifera and 

 Ostracoda, etc., from marine deposits, and seeds of plants from 

 comparatively modern fresh-water deposits. 



. 4. When a formation contains nodules or concretions, special 

 attention ought to be paid to these. They have usually been 

 formed round decaying organic matter, and a large proportion of 

 the best-preserved fossils occur in them. 



The clay-ironstone nodules found in the beds associated with 

 seams of coal usually contain remains of coal plants, insects, and 

 Crustacea enclosed within them, often of great beauty. 



Many concretions enclose fossil fishes. The late Mr. Charles 

 Moore found, after long experience, that the nodules of White Lias, 

 containing fishes, were most successfully opened by first breaking 

 them in two near the centre, and then splitting open each half 

 at the inner transverse fracture. The two halves of the split 

 surfaces were afterwards glued together. 



The interior of chalk flints and nodules of chert from the Green- 

 sand frequently have hollows containing loose whitish or greenish 

 powder. This should be collected, for it usually has small organisms 



