236 " NEW YORK STATE MUSEUM 



the arrangement of the materials, as they show a more or less strati- 

 form or bedded structure which is absent from till of the ground 

 moraine. A third method of occurrence is represented by the sands 

 and gravels along the beaches of the glacial lakes that came into 

 existence in the closing stages of the Pleistocene after the withdrawal 

 of the ice. Here the materials are characterized by a uniformity 

 of physical features by reason of the efficient sorting action of the 

 shore waters that is comparable to that of beach sands along our 

 present coasts. Glacial Lake Iroquois, which occupied the basin 

 of Lake Ontario but spread far beyond the present limits of its 

 waters, has the largest of these beach deposits. In the Hudson and 

 Champlain valleys the glacial waters also rose to high levels and 

 have left behind a series of bedded sands, gravels and clays which 

 are easily to be discriminated from the morainal and outwash deposits 

 directly contributed by the ice. 



In the beaches of Long island and Staten island are found more 

 recent deposits of sand and gravel that have economic importance. 

 Their materials, however, are largely derived from the glacial 

 moraines which extend across the islands from the Connecticut to 

 the New Jersey mainland and which mark the most southerly limit 

 of the Pleistocene ice sheet. As compared with the morainal sands 

 they are much better graded both in size and character of material, 

 and their field of usefulness is much increased. Smaller beaches of 

 present-day formation occur on the shores of the interior lakes. 



Building sand. In this class are included the loose sands and 

 gravels employed in making mortar, concrete or artificial stone for 

 engineering work and buildings. A large variation in composition 

 and physical properties may be found in such sands, and in fact 

 almost any deposit that contains a fair percentage of hard particles, 

 not too fine in grain, whether of quartz or of undecomposed rock, 

 may be employed where the conditions of service are not very rigid. 

 The resources consequently are more extensive than of sands for 

 special employment, and little attention has been given heretofore 

 to their investigation. 



It is to be noted in this connection that sands are actually an 

 important factor in determining the quality of the concrete for 

 which they are used, and the tendency in engineering work is toward 

 the careful selection of both sand and the coarser aggregates. To 

 be suitable for dependable structures a sand should be practically 

 pure quartz, free of clayey admixture or of shale particles which 

 shrink or swell imder changing atmospheric conditions. The texture 

 of sand is also important but the requirements in this respect vary 



