THE CHARACTERISTICS OF VARIOUS TYPES OF 
CONGLOMERATES: 
GEORGE R. MANSFIELD 
Harvard University 
In the prosecution of a recent study of the Roxbury Conglomerate 
(Boston, Mass.), the writer found himself in need of criteria by which 
to determine the mode of origin of that formation. A critical exami- 
nation was therefore made of the published descriptions of conglom- 
erates in many parts of the world and belonging to many geological 
ages, in the hope of discovering characteristics sufficiently marked to 
distinguish one type from another. The data collected and the con- 
clusions derived therefrom have recently been published in detail.? 
The present paper is a brief summary of the results of the investigation. 
Five general types of conglomerate were ‘considered, namely: 
marine, fluviatile, estuarine, lacustrine, and glacial. In addition to 
these, another type was.studied, commonly known as crush-conglom- 
erate, but really pseudo-conglomeratic in its nature. The fact was 
recognized that many conglomerates are the product of the combined 
action of several conglomerate-forming processes, but the results of 
each process were classified separately. 
Among the formations taken under consideration were: the Cre- 
taceous formation of ‘Texas, as described by Hill;3 the Pottsville Con- 
glomerate; non-marine formations in India, Persia, Great Britain, 
and the United States; the Devonian of Pennsylvania and Maryland, 
as described by Willis; the Newark formation as described by 
Russell;5 glacial deposits of the Quaternary period in the United 
States and Europe; ancient glacial deposits in India, Australia, South 
Africa, and Norway; and crush-conglomerates in the Isle of Man and 
Argyllshire. 
t Read before the Geological Society of America, December 28, 1906, New York. 
2 Museum of Comparative Zodlogy, Bulletin No. X LLX, Geological Series, 8, 1906. 
3 R. T. Hill, US. Geological Survey, Twenty-first Annual Report, 1901, pt. 7. 
O38 Maryland Geological Survey, 1902, Vol. IV, pp. 21-93. 
5 U. S. Geological Survey, Bulletin No. 85, 1892. 
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