Charles Thomas Jackson. — Woodworfh. 83 
hearers Louis Agassiz, Jeffries Wyman, T. T. Bouve, T. Ster- 
ry Hunt, and numerous younger men, among whom tlie names 
of LeConte, Slialer, Niles, Hyatt, and others are recorded in 
the reports of these meetings. 
On these ocassions, Dr. Jackson was ever ready with ques- 
tions and remarks elicited by the papers of others, when his 
own abundant labors were not the subject of discussion. Tlie 
store of his ready information and the range of his interests 
and investigations are shown b}' the list of his remarks pub- 
lished in the biographical notes appended to this paper. 
To the geologist, the records of these gatherings afford a 
clearer insight into Dr. Jackson's views on many questions 
than do his special works upon areal geology. His idea of the 
origin of elongated pebbles in conglomerates through the shap- 
ing action of waves on a beach, his general denial of belief in 
the glacial theory of professor Agassiz, his disavowal of the 
derivation of igneous rocks through the fusion of sediments 
in tl)e ultra-stages of metamorphism, are conclusions which 
find a place in these proceedings along with the propositions 
and rejoinders of his able associates. From time to time he 
made more important contributions to the publications of the 
society. 
Dr. Jackson did not always push his theories of geftlogical 
phenomena to tiie fullness of conclusion and statement which 
would enable us at the present day fully to understand them. 
He had too many irons in the fire to do as he would with all 
of them. Here and there, as in the chance remarks of many 
of the older geologists, we find the germs of theories which 
have since been prominently advocated. In discussing the 
joints of the Roxbury conglomerates, near Boston, he antici- 
pates Crosby's elaborated thesis, by suggesting that earth- 
quake shocks might have been the cause of the phenomena. 
He pointed out a criterion for distinguishing ice-borne 
from water-transported detritus, the first remaining coarse 
up to the limit of distribution, the second decreasing in size 
of the particles as the distance from the original source in- 
creased. This point has since been made out in the study of 
glacial phenomena in the Alps. 
Although an advocate of deformation of the crust by the 
agency <^»f internal heat, he put forth the idea which in its 
