218 J. E, Marr—Some Effects of Pressure. 
obviously quite distinct from any of the foregoing, but which are 
not sufficiently well preserved to admit of description. They consist 
of thin plates, from half to three-fourths of an inch in thickness, 
which had nearly an upright position, and have calices, all of which 
are oblique. ‘They were found in the neighbourhood of Evesham. 
DESCRIPTION OF PLATE VII. 
Fie. 1. Heterastrea Etheridgei, a horizontal section a little below the calice, show- 
ing the imperfect union of the corallites, fissiparity in pro- 
gress in two corallites, and one corallite which has resulted 
from gemmation. Magnified three diameters. 
BH ee Ep Etheridgei, a vertical section showing the dissepiments and the 
edges of the septa. Magnified three diameters. 
59. Be ae Eveshami, a portion of the type specimen showing a calice 
which has been developed from a bud, and still retains a 
more or less circular outline. Magnified two diameters. 
ae ee 90 Fromenteli, a portion of the specimen figured by Prof. Duncan, 
exhibiting, in close proximity, both gemmation and fissi- 
parity. Magnified two diameters. 
pp) | B09 B55 Tomesi, portions having calices resulting from both gemmation 
and fissiparous division. Magnified two diameters. 
POMC si9 regularis, some calices magnified two diameters. 
59. be 36 Stricklandi, some calices of a specimen from Evesham, having 
both gemmation and fissiparous division. Magnified two 
diameters. 
pp oe 30 endothecata, a portion of the type specimen, showing fissiparous 
division in progress. Magnified two diameters. 
IJJ.—On Somes Errects or Pressur& ON THE DEVONIAN SEDIMENTARY 
Rocks or Nortu Devon.! 
By J. E. Marr, M.A., F.G.S. 
URING Professor Hughes’ annual geological excursion, which 
was last Easter conducted to Ilfracombe, I was much struck 
with certain structures exhibited by the ordinary Devonian sediments, 
and some of these are, I think, worthy of a short notice. Most of 
them are exhibited on the beach close to Ilfracombe, at the bath- 
ing place, where there is also seen the folded grit band rendered 
classical through Dr. Sorby’s writings. ; 
The rocks here consist of cleaved argillaceous deposits interstrati- 
fied with thin grits and limestones, and the latter have been folded 
amongst the former in a most remarkable manner. The changes 
which take place are illustrated in Fig. 1. The first stage is the 
production of a series of sigmoidal folds having the middle limb 
replaced by a thrust-plane. This is well shown in the case of two 
limestone bands just above a small cave on the shore, at the bathing 
place. A further development is shown in Fig. la, and the result of 
this is the formation of a series of ‘“‘eyes”’ of limestone, which vary 
in length from a fraction of an inch to several feet, according to the 
magnitude of the folds. As the smaller folds are merely the con- 
voluted portions of larger ones, the “eyes” get pulled out along the 
thrust-planes, replacing the middle limbs of the larger folds, as shown 
in Fig. 1b. In this way, the central portions of these larger folds 
1 Read at the Manchester Meeting of the British Association. 
