204 [Assembly 



go on for a long time, without seriously affecting the texture of the 

 stone, producing no important result beyond the unsightly appear- 

 ance. Generally, however, the decomposition of the pyrites pro- 

 duces the gradual destruction of the stone. 



We have in the State of New York a class of argillaceous sandstones 

 largely in use as building stones, and which are less known in any 

 otlier State. They are of the character of rocks formerly known as 

 " GraywackeP and the name might be usefully retained to designate 

 the argillaceous sandstones of the Hudson river group, the Hamilton, 

 Portage and Chemung groups. These beds of the Hudson river 

 group are known as hlue stone, which is a compact argillaceous 

 sandstone consisting of variable proportions of these materials. 



The name hlue stone is equally applicable to the heavy-bedded 

 compact arenaceous layers, and the thin-bedded slaty layers, which 

 are largely used in the foundations of ordinary buildings. Much of 

 the heavy-bedded slaty rock of this character, which is cpiarried 

 along the Hudson river valley, belongs to the Quebec group ; but I 

 am not at this time aware of any quarries in the same formation, 

 which furnish dressed building stone. 



In the Hudson river group, this rock occurs in many localities, in 

 very regular beds which are cut by vertical joints presenting clean, 

 straight faces, and are thus laid in the building. The composition 

 of these stones (that is, in the proportions of silica and alumina) 

 often varies in the distance of a few rods; but, if well selected and 

 laid on its natural bedding, it makes a durable building material. 

 Much of it, however, becomes stained from the decomposition of iron 

 pyrites, which after a length of time, either leaves the surface of a 

 permanently rusty brown color, or the decomposition goes on till 

 the rock crumbles or scales off in thin laminae. Sometimes the 

 faces of the joints are coated by thin laminae of carbonate of lime, 

 arising from the solution and infiltration of calcareous matter; and 

 this forms a permanent coating, which resists all further change from 

 atmospheric influences. It is of the greatest importance that these 

 stones be carefully selected, or otherwise they soon become disin- 

 tegrated. 



The flagstones, so abundantly supplied from the upper part of the 

 Hamilton group and lower ]3art of the Portage group, are among 

 the most enduring of the compounds of silica and alumina. The 

 material is a fine-grained compact argillaceous sandstone of a blue or 

 grayish-blue color, which, when free from seams, is scarcely in- 

 fluenced by the action of the weather. These beds are not only used 

 for flagstones in most of the Atlantic cities, but in Al])any, Troy, 

 and other towns along the river and elsewhere, this stone is used for 

 door-steps and caps, window-sills and caps, water tables, etc. The 

 stone is very strong and durable, sometimes slight!}' staining from 

 the decom])osition of iron pyi'ites, but rarely or never undergoing 

 disintegration from that cause. 



The blue stone of Maiden on the Hudson river, which has of late 

 come into use for ashlar, door-steps and sills, pillars or pilasters, 

 window-sills and caps, water tables, etc., is obtained from some 



