AVGIST 14, 1003.] 



SCIENCE. 



213 



NOTES ON THE GEOLOGY OF LONG ISLAND.* 



In the investigation of the underground 

 water resources of Long Island, v,-hich has re- 

 cently been undertaken by the Division of 

 Hydrology, U. S. Geological Survey, a num- 

 ber of new points have been developed which 

 are of interest at this time. Among these 

 are: 



1. Proof of the absence of a uniform ' blue 

 clay floor.' 



2. The presence of deposits of an earlier ice 

 advance which indicate old deeply buried 

 channels extending 225 feet below sea level. 



3. The presence of erosion remnants of a 

 topography of pre-Pleistocene origin extend- 

 ing undisturbed to a height of at least 360 

 feet above sea level. 



4. The considerable number of deep flowing 

 wells on the north shore. 



The idea that there is a fairly uniform bed 

 of blue clay of probable Chesapeake Miocene 

 age, which dips gently southward from its 

 outcrop on the north shore has been demon- 

 strated incorrect by well records obtained 

 through the work of the Commission on Addi- 

 tional Water Supply, and from other sources. 

 These have also indicated that that part of the 

 clay bed which underlies the southwestern 

 part of the island is Pleistocene since it is 

 underlaid by glacial beds. Several clay beds 

 of different age have evidently been connected 

 in the attempt to get a clay bed having a 

 stratigi-aphic unity. 



The examination of well samples, particu- 

 larly those from the test wells of the Brooklyn 

 Water Works, has shown in the southern part 

 of the island, west of Valley Stream, old gla- 

 cial deposits lying uuconformably on an old 

 topography, and separated from the recent 

 glacial material by thick beds of blue clay and 

 sands not of recognizable glacial origin. In 

 the western part of Brooklyn these older gla- 

 cial beds have been found at a depth of 225 

 feet helow sra level, and are believed to throw 

 important light on the question of early Pleis- 

 tocene elevation and subsequent submergence, 



* Publislied by' permission of the Director of the 

 U. S. Geological Survey. 



as well as on the position of former stream 

 valleys. 



The last ice advance found a rather irregu- 

 lar topography and succeeded in covering the 

 older hills with a veneer which is for the most 

 part quite thin. Along the backbone of the 

 island these deposits are much thinner than 

 has been supposed, the really prominent por- 

 tions of the ridge seeming to owe their prom- 

 inence more to the preglacial hills than to 

 morainic deposits. The most marked example 

 of this is in the West Hills, lying in the 

 center of the island, between Farmingdale, 

 Melville, Cold Spring Harbor and Hicksville. 

 Here there is a marked southward tongue of 

 hills projecting from the east and west ridge. 

 Glacial material covers the northward slope, 

 and reaches a height of over 400 feet; but the 

 southern portion of the ridge has not been 

 covered with ice and is clearly not glacial. 

 The following section just west of Melville 

 indicates something of its structure. 



SECTION JUST WEST OF MELVILLE, NEW YORK. 



Top of section about 300 feet A. T. I'eet 



1. Horizontally bedded yellow sand and 



quartz gravel with a few verj- much 

 weathered compound pebbles. Xear 

 the upper part of the section the 

 gravel is very bright orange 38 



2. Covered 3 



3. Dark-colored, lavender, green and black 



sandy clay, weathering yellow 6 



4. Horizontally bedded, finely laminated, red 



arkose with a few rounded quartz peb- 

 bles. Weathering product of bed be- 

 low 2. .5 



5. Horizontally bedded, finely laminated, 



green, white and pink arkose 3 



G. Ferruginous sandstone 0.3 



7. Yellow sand with ferruginous plates.... 0.5 



8. Irregularly bedded, gray, clayey sand 



blotched with red and yellow becoming 

 more sandy above and passing into n 

 pink or red sand with lens-shaped 

 masses of white clay !>..'> 



9. Covered 0..5 



10. White clayey sand with large quartz 



gravel 2 



1 1 . Covered 1 



12. Stratified orange-colored .sandy clay with 



ferruginous plates 1 



