264 The Ajuaicaii Geologist. October, i«e*; 
The Cambrian sediments were first strongly folded and injected 
by the pre-granitic diabase; and quite certainly not later than the 
early Devonian epochs they were invaded by the great body of magma 
from which the granitic series was developed. No trace of the floor 
upon which the Cambrian strata were deposited has been discovered 
in the region of the Blue IJills complex. It is believed that the gran- 
itic magma was, in the main, developed in situ by a great heat invasion 
or rising of the isogeotherms inaugurated by deep sedimentation and 
greatly stimulated or accelerated by the thickening of the supercrust 
by extreme plication and flowage and the transformation of mechani- 
cal energy into heat. This heat invasion was sufficient to induce 
aqueo-igneous fusion in the lower portion of the hydrated zone, 
whereby the pre-Cambrian rocks and a considerable volume of the 
overlying Cambrian sediments were absorbed by the plutonic magma. 
During the slow refrigeration of the batholite and the solidification of 
the magma, it experienced both chemical and textural differentiation; 
but the chemical differentiation, whether of the main body of the 
batholite or of its contact zone, was practically limited to the great- 
est depths and dependent upon a convectional circulation of "the 
magma, in accordance with Becker's theory of fractional crystalliza- 
tion. In conformity with this view, the contact zone is composed, 
at successively greater original depths, of quartz porphyry,, fine gran- 
ite, granodioryte, and dioryte, each of these contact types passing 
gradually downward into the normal granite. After long continued 
erosion had in large part removed the sedimentary cover of the bath- 
olite, crustal adjustments permitted the extrusion of a part of the 
deep-seated and relatively acid magma residuum, forming intrusive 
masses or dikes of microgranite and aporhyolyte and efifusive masses 
or surface flows of compact and fluidal forms of aporhyolyte. 
This general theory of the complex closely parallels, at most 
points, that proposed by Dr. A. C. Lawson for the complex of sedi- 
mentary and granitic rocks in the Rainy Lake region (Geol. Surv. 
Canada, Annual Report, new series, vol.iii, 1887-88, F, 139-142). 
25. Paleontologyof the Cambrian Terranes of the Boston Basin. 
By Amadeus W. Grabau, Boston, Mass. The Lower Cambrian 
rocks are found to contain fossils at Nahant, Mill Cove, Rowley, 
Topsfield, and Jeffreys Ledge. The last three localities were dis- 
covered by Mr. J. H. Sears, who was also the first discoverer of fos- 
sils at Nahant (1887). From collections made by Mr. Sears at Na- 
hant, seven species have been identified, including four of Hyolithes. 
The fossils detected in the rocks of the other localities consist of 
indeterminate sections of Hyolithes, and a cross-section of a trilobite 
from Mill Cove. From pebbles and boulders found at Nahant and 
Cohasset by Mr. T. A. Watson, a large number of Lower Cambrian 
fossils have been obtained, representing fifteen species. 
The Middle Cambrian of Hayward's creek. South Braintree, con- 
tains the large Paradoxides harlani, Agraulus quadrangularis, and 
