22 NEW YORK STATE MUSEUM 



quarry has its own characteristic reeds. Berkey 1 states from 

 observation of the bluestone in the Catskills that the capacity for 

 splitting into slabs depends upon the abundance, arrangement and 

 size of the elongated and fibrous grains. The reeds are marked by 

 a darker color and finer grain than the body of the rock. The 

 structure is partly original and partly arises from changes subse- 

 quent to the formation of the bluestone, whereby the fibrous ap- 

 pearance has been accentuated. 



The massive igneous rocks, of course, are devoid of any capacity 

 for cleavage comparable to that in bedded types. But none the 

 less, they oftentimes possess a differential parting which greatly 

 facilitates their manipulation in the quarry. Quite commonly the 

 parting takes place in two directions at right angles to each other. 

 The line along which the stone yields most readily is known as 

 the rift ; it may lie in any plane, but is more often, perhaps, nearly 

 vertical. The direction of the second easiest cleavage is called 

 the " grain " or sometimes the " run." Though many quarry stones 

 seem to possess only the two lines of smooth fracture, there is 

 occasionally a third, along which they may be broken with some 

 degree of ease and which is known as the " head." This is less 

 easily detected than the others, because it approaches the normal 

 fracture of the stone. 



Rift and grain are frequently described in works on the quarry 

 industries with special reference to the granites. From the in- 

 formation given, the impression might be gained that these struc- 

 tures are only characteristic of the granites, though such con- 

 clusion is by no means warranted. The syenitic rocks of the 

 Adirondacks often show a fairly good cleavage in two directions. 

 Other examples of rift which may be compared with the same 

 structure in granites are to be found in the crushed but 

 massive-appearing anorthosites, such as those quarried in the north- 

 ern Adirondacks, near Ausable Forks and Keeseville. This rock 

 is almost entirely made up of lime-feldspar (labradorite) though 

 some phases contain quite a little pyroxene and garnet. It splits 

 readily in two directions so as to be easily dressed into dimension 

 stone or paving blocks. The igneous rocks of the gabbro class, in 

 which large percentages of pyroxene or amphibole are present, 

 seem to lack the structure in anything like the typical development 

 of the more acid rocks. 



1 Quality of the Bluestone in the Vicinity of Ashokan Dam. School of 

 Mines Quarterly, v. 29, no. 2, p. 156-57. 



