Know all by these presents, that the undersigned hereby
constitutes and appoints each of Robert L. Seelig,
Executive Vice President & General Counsel,
Jennifer L. Moyer, Managing Director & Corporate
Secretary, Jason R. Lichtenstein, Managing Director
& Associate General Counsel, and Wesley Bell,
Vice President & Assistant General Counsel,signing
singly, the undersigned's true and lawful
attorney-in-fact to:
(1) execute for and on behalf of the undersigned, in the
undersigned's capacity as an officer and/or director of White
Mountains Insurance Group, Ltd. (the "Company"), Forms 3, 4,
and 5 in accordance with Section 16(a) of the Securities
Exchange Act of 1934 and the rules thereunder;
(2) do and perform any and all acts for and on behalf of the
undersigned which may be necessary or desirable to complete
and execute any such Form 3, 4, or 5, complete and execute
any amendment or amendments thereto, and timely file such form
with the United States Securities and Exchange Commission and
any stock exchange or similar authority; and
(3) take any other action of any type whatsoever in connection
with the foregoing which, in the opinion of such attorney-in-fact,
may be of benefit to, in the best interest of, or legally
required by, the undersigned, it being understood that the
documents executed by such attorney-in-fact on behalf of the
undersigned pursuant to this Power of Attorney shall be in
such form and shall contain such terms and conditions as such
attorney-in-fact may approve in such attorney-in-fact's discretion.
The undersigned hereby grants to each such attorney-in-fact full
power and authority to do and perform any and every act and thing
whatsoever requisite, necessary, or proper to be done in the
exercise of any of the rights and powers herein granted, as
fully to all intents and purposes as the undersigned might or
could do if personally present, with full power of substitution or
revocation, hereby ratifying and confirming all that such
attorney-in-fact, or such attorney-in-fact's substitute or
substitutes, shall lawfully do or cause to be done by virtue of
this power of attorney and the rights and powers herein granted.
The undersigned acknowledges that the foregoing attorneys-in-fact,
in serving in such capacity at the request of the undersigned,
are not rendering legal advice of any form, other than satisfying
regulatory filing requirements, with respect to any transactions
to be reported on Forms 3, 4 and 5 are not assuming, nor is the
Company assuming, any of the undersigned's responsibilities to
comply with Section 16 of the Securities Exchange Act of 1934.
The undersigned hereby grants this Power of Attorney with the
understanding that information provided to each such
attorney-in-fact is strictly confidential and will not be
disclosed to senior management, directors or other third parties
whether affiliated or otherwise and will be used solely to
complete and execute any such Form 3, 4 or 5, complete and
execute any amendment or amendments thereto, and timely file
such form with the United States Securities and Exchange Commission
and any stock exchange or similar authority.
This Power of Attorney shall remain in full force and effect
until the undersigned is no longer required to file Forms 3,
4, and 5 with respect to the undersigned's holdings of and
transactions in securities issued by the Company, unless
earlier revoked by the undersigned in a signed writing
delivered to the foregoing attorneys-in-fact.
IN WITNESS WHEREOF, the undersigned has caused this
Power of Attorney to be executed as of the date indicated
below.

Date: May 24, 2018     /s/  G. Manning Rountree