252 DR. A. GTLLIGAJNT ON THE PETROGRAPHY OE [vol. lxXV, 



datum-line. The top of the series has been taken at the top of the 

 Hough liock, where it can be seen to be overlain by the Lower 

 Coal Measures, as at Whitehall Quarries, Horsforth, near Leeds. 

 However, as no questions of correlation are involved in this work, 

 the exact delimitations of the various beds is a matter of minor 

 importance. 



The Millstone Grit Series covers an area in Yorkshire alone of 

 no less than 840 square miles, and is important physiographically, 

 as it forms the capping of most of the hills of the Pennine Chain, 

 such as Mickle Fell, Whernside, Ingleborough, Penygent, etc., and 

 by its presence there preserves the more easily denuded strata below 

 from a more rapid destruction. 



Economically the formation is of great importance, being ex- 

 tensively quarried for building purposes in the districts where it 

 occurs, its value for this purpose being well understood by the 

 Saxons and Normans, who used it in the construction of some of 

 their noblest work. As the name implies, a brisk trade was at one 

 time carried on in the making of millstones and grindstones from 

 the grits and sandstones, their use for such purposes dating back 

 to very early times. It also yields an excellent artesian supply of 

 water, many boreholes for public and private works having been 

 made into this rock, and it is for this purpose being more exploited 

 than ever in the neighbourhood of Leeds, Bradford, Huddersfield, 

 and other large Yorkshire towns. 



While, however, it has been generally known and valued for the 

 purposes that I have mentioned, it has been undeservedly neglected 

 by geologists as a subject for study from a purely scientific point 

 of view. True it is that much excellent work has been done by 

 Dr. Wheelton Hind, Dr. Wellburn, and others upon the marine 

 fauna of the shales, but much more still remains to be done. The 

 first and, so far as I am aware, the only worker to attack seriously 

 the question of source and origin of the material making up this 

 important series of rocks was the late Dr. Henry Clifton Sorby, 

 who read a paper upon this subject before the Yorkshire Geo- 

 logical & Polytechnic Society at its Annual Meeting in Leeds, 

 March 17th, 1859. Since the publication of that paper, no syste- 

 matic work has been done along the same lines until the present 

 research was undertaken. 



The methods of investigation made use of by Sorby have in a 

 large measure been followed by me ; but, in addition to the exami- 

 nation of the coarser material composing the conglomerates and 

 grits, the finer material of the shales and the heavy minerals 

 obtained from the various beds have also been examined. Further, 

 the area laid under contribution for material for this research has 

 been much more extensive than that covered by Sorby. It will, 

 however, be seen that the results of my enquiry corroborate in 

 a remarkable way the conclusions arrived at by that eminent 

 geologist. 



