part 4] THE MILLSTONE GBIT OF rORK SHIRE, '2~>9 



The quarrymeD engaged in working the various grits are only 

 too familiar with the frequent occurrence of discoidal masses of 

 shale, which are often in such numbers as to render worthless the 

 large blocks for which the beds arc worked. I have examined 

 a great number of these, and have found them to he of ordinary 

 micaceous shale, exactly similar to the shales of Carboniferous age 

 such as the Yoredales or Millstone Grit. In a large specimen 

 found in the Rough Rock at Horsforth, fossil plant-remains have 

 been obtained. These were submitted to Dr. R. Kidston, F.K.S.. 

 who pronounces them to be Cordcit( j s borassifolius. The origin of 

 these shale-masses is somewhat obscure. Do they represent small 

 mud-puddles infilled at the time of the accumulation of the sur- 

 rounding coarse material, or are they true pebbles derived from a 

 consolidated shale ? The small masses, 1 inch or less in diameter, 

 lie in all directions in the grit ; they seem to be transported, 

 and may possibly represent fragments of clay-slate or a similar 

 rock, indeed one such piece has actually been found. The larger 

 pieces lie more or less parallel to the bedding, and seem to be of 

 contemporaneous origin. Furthermore, these latter have the 

 impress of the surrounding grit, while many of the smaller pieces 

 are quite smooth. 



III. Examination of the Fixer Material. 



The Millstone Grit has been described as an arkose, and no 

 better name could be employed, as it is neither more nor less than 

 a disintegrated granitoid rock which has been reconsolidated. 

 F$The rocks which have contributed the material were certainly 

 acid in composition, the quantity of minerals characteristic of basic 

 rocks being of such an order of magnitude as to be quite negligible. 

 A cursory examination of a hand-specimen of the grit shows 

 quartz and felspar, with occasional flakes of mica and often 

 garnet. While, however, mica is not so commonly found in the 

 coarser beds, it is of such abundance in some cases as to make up 

 beds of practically pure micaceous material 2 to 3 feet thick, such 

 as that below the liough Rock of Keighley Moor; while in the 

 flaggy beds it determines the planes of division. 



(1) Quartz. 



The grains vary greatly in the degree of angularity, many being 

 quite rounded in some of the lower beds (those examined from the 

 Kinderscout Beds of Upper Wharfedale show several rounded 

 grains) and also in some of the Middle Grits, such as that of 

 St. Helen's Quarry, Spofforth (Pollifool Grit). In the Rough 

 Rock very few have been found: indeed, they may be described as 

 rare. Much of the angularity is. however, due to a deposit of 

 secondary silica upon the original grain, as is so well seen on the 

 surfaces of the larger pebbles of quartz. It may here be noted 

 that the quartz-grains found in a sandstone near the top of the 

 Carboniferous Limestone at Kofi Beck, Appleby, and quiti 



