In reliance on the apportionment concept the Court has at various times
sustained, in the case of a sleeping car company, as we have seen, a
valuation based on the ratio of the miles of track over which the
company runs within the State to the whole track mileage over which it
runs;[664] in the case of a railroad company, a valuation based on the
ratio of its mileage within the State to its total mileage;[665] in the
case of a telegraph company, a valuation based upon the ratio of its
length of line within the State to its total length;[666] in the case of
an express company, as we have just seen, a valuation based upon the
ratio of miles covered by it in the State to the mileage covered by it
in all States.[667] Also, a tax has been upheld as to a railroad line
whose principal business was hauling ore from mines in the taxing State
to terminal docks outside the State, where the line and the docks were
treated by the railway as a unit, the charge for the dock service being
absorbed in the charge per ton transported; and where the evidence did
not show that the mileage value of the part of the line outside of the
taxing State, with the docks included, was greater than the mileage
value of part within it.[668] Nor does the commerce clause preclude the
assessment of an interstate railway within a State by taking such part
of the value of the railroad's entire system, less the value of its
localized property, such as terminal buildings, shops and nonoperating
real estate, as is represented by the ratio which the railroad's mileage
within the State bears to its total mileage.[669] To the objection that
the mileage formula was inapplicable in this instance because of the
disparity of the revenue-producing capacity between the lines in and out
of the State, the Court answered that mathematical exactitude in making
an apportionment had never been a constitutional requirement.
"Wherever," it explained, "the State's taxing authorities have been held
to have intruded upon the protected domain of interstate commerce in
their use of a mileage formula, the special circumstances of the
particular situation, in the view which this Court took of them,
precluded a defensible utilization of the mileage basis."[670] The
principle of apportionment is, moreover, applicable to the intangible
property of a company engaged in both interstate and local commerce, as
well as to its tangible property.[671]

APPORTIONED GROSS RECEIPTS TAXES

Th