Correspondence — Mr. James W. Davis. 191 



he has been able to examine 19, and finds that they have been 

 needlessly multiplied, owing especially to the neglect on the part of 

 describers to allow for difference in the structure at various stages 

 of growth and in different parts of the polyzoarium. His investiga- 

 tions led him to refer the forms known to bim to only 5 species, 

 namely, Fenestella plebeia, M'Coy, F. crassa, M'Coy, F. polyporata, 

 Phill., F. nodulosa, Phill., and F. membranacea, Phill. 



COIRIEaiESIFOIN-IDIEIsrCIE:. 



THE CALDER VALLEY. 



Sir, — Will you permit me to thank my friend Mr. Dakyns for 

 drawing the attention of your readers to two or three particulars 

 having reference to the physical forces which have caused the con- 

 figuration of the Valley of the Calder. He is puzzled by the 

 statement tbat heather and peat are found above sandstones, and that 

 the heather does not grow on limestones or shale or clay, further 

 observing that he has generally noticed the peat underlain by a bed 

 of yellowish clay, very similar to the underclay of a coal-seam. Of 

 course, Mr. Dakyns is correct. I do not suppose any one would 

 expect to find any plants, except lichens, growing on a bare mass of 

 rock. The disintegration of the sandstone by atmospherical agencies, 

 and the decay of organic matter, will tend to form a soil in which 

 the heather can take root, and which may eventually assume the 

 appearance indicated by Mr. Dakyns. Taking the facts, however, 

 in the broad sense which I intended in the paper, we do find that 

 the heather grows only on the moorlands constituted of sand or 

 gritstone. I could quote numerous instances where a sharp line can 

 be drawn between the sandstones and shales which form the surface 

 stratum, by the occurrence or otherwise of heather growing above it, 

 and I am sure it is unnecessary to remark that heather is not a 

 characteristic plant on limestones. 



I did not intend that any geological beginner should imagine that 

 the' present faces of the corresponding escarpments of the Yorkshire 

 and Lancashire grits were ever in contact, and I venture to think 

 that the purport of the paper will show that a constant change of 

 form is in progress, and that the rock escarpments are always subject 

 to the disintegrating action of water or frost. There can be little 

 doubt, also, that the original faces of the rocks would be borne 

 further and further from the centre of operations at the time that 

 the elevation took place, and that some part of the distance by which 

 the opposing escarpments are separated at present is due to this 

 cause. 



I am afraid my reasons for considering that the drift or gravels in 

 the Valley of the Calder have been transported to their present 

 position during a period of submergence would occupy more space 

 than could be devoted to a letter, and with your kind permission I 

 will defer stating them to some future time. 



Chevinedge, Halifax, February 19th, 1879. James W. Davis. 



