1897.] NEW YORK ACADEMY OF SCIENCES. 227 



The Millstone Grit Series is separated into four divisions : 

 First Grit or Rough Rock, Second Grit or Haslingden Flags, 

 Tliird Grit, Fourth Grit or Kinder Scout Rock. 



The series reaches its maximum development in Lancashire, 

 where it attains a thickness of 5,000 feet. 



First Grit or Rough Rock. — A massive coarsely felspathic grit, 

 sometimes containing a seam of coal eighteen inches thick. 



Second Grit or Haslingden Flags. — Well bedded, finegrained 

 sandstones and flags extensively quarried for building stones, 

 paving stones, flags, etc. 



Third Grit (^Brooksbottom Series). — A very changeable series 

 -of sandstone and shales with a few thin coals. In some localities 

 the sandstones swell out into massive bedded grit rocks, whilst 

 in other cases they are insignificant and shales predominate. 



At Greens Clough (Beaters Clough of the Ordnance Maps), 

 near Burnley, a bed of sandstone 60 feet thick, which belongs to 

 this division, has been quarried. It is rich in casts of the trunks 

 of Calamites, Sigillaria and Lepidodendra. Immediately above 

 it occurs a 3-inch coal. 



Fourth Grit or Kinder Scout Rock. — Coarse sandstones and 

 grits, with, in one case (Rawenstall, near Manchester), a 6 inch 

 seam of coal. 



The grits occasional!}^ become so coarse as to resemble con- 

 glomerate. 



It must be borne in mind that the Millstone Grits of Lanca- 

 shire form but a small portion of an extensive mass of sandstones 

 and shales which occupy the high ground of the West-Riding of 

 Yorkshire and stretch southwards and eastwards to the hill 

 country of Derbyshire. Taken as a whole, these grits and shales 

 represent a period of great subaerial denudation of a land surface 

 largely made up of the older crystalline rocks, and a correspond- 

 ing sedimentation along the borders of the old Carboniferous 

 limestone sea, producing a shallowing of that sea and eventually 

 a lagoon-like belt, upon which the later Coal Measure forests 

 found a suitable place. 



The Lancashire Coal Measures which accumulated upon the 

 substructure of grits and shales, are divided into the lower, 

 middle and upper series, but the boundary lines are purely arbi- 

 trary and drawn for convenience rather than as indicating any 

 real change in the deposits or their contents. 



Speaking generallj^ the Lower Coal Measures are specially 

 marked by shales containing supposed marine forms of life, thick 

 beds of grit and but few and thin coals. The Middle Coal 

 Measures form the productive measures, marine bands with a 

 tsingle exception being absent. 



